linux/drivers/comedi/comedi_buf.c

691 lines
18 KiB

staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: use dma_mmap_coherent for DMA-able buffer mmap Comedi's acquisition buffer allocation code can allocate the buffer from normal kernel memory or from DMA coherent memory depending on the `dma_async_dir` value in the comedi subdevice. (A value of `DMA_NONE` causes the buffer to be allocated from normal kernel memory. Other values cause the buffer to be allocated from DMA coherent memory.) The buffer currently consists of a bunch of page-sized blocks that are vmap'ed into a contiguous range of virtual addresses. The pages are also mmap'able into user address space. For DMA'able buffers, these page-sized blocks are allocated by `dma_alloc_coherent()`. For DMA-able buffers, the DMA API is currently abused in various ways, the most serious abuse being the calling of `virt_to_page()` on the blocks allocated by `dma_alloc_coherent()` and passing those pages to `vmap()` (for mapping to the kernels vmalloc address space) and via `page_to_pfn()` to `remap_pfn_range()` (for mmap'ing to user space). it also uses the `__GFP_COMP` flag when allocating the blocks, and marks the allocated pages as reserved (which is unnecessary for DMA coherent allocations). The code can be changed to get rid of the vmap'ed address altogether if necessary, since there are only a few places in the comedi code that use the vmap'ed address directly and we also keep a list of the kernel addresses for the individual pages prior to the vmap operation. This would add some run-time overhead to buffer accesses. The real killer is the mmap operation. For mmap, the address range specified in the VMA needs to be mmap'ed to the individually allocated page-sized blocks. That is not a problem when the pages are allocated from normal kernel memory as the individual pages can be remapped by `remap_pfn_range()`, but it is a problem when the page-sized blocks are allocated by `dma_alloc_coherent()` because the DMA API currently has no support for splitting a VMA across multiple blocks of DMA coherent memory (or rather, no support for mapping part of a VMA range to a single block of DMA coherent memory). In order to comply with the DMA API and allow the buffer to be mmap'ed, the buffer needs to be allocated as a single block by a single call to `dma_alloc_coherent()`, freed by a single call to `dma_free_coherent()`, and mmap'ed to user space by a single call to `dma_mmap_coherent()`. This patch changes the buffer allocation, freeing, and mmap'ing code to do that, with the unfortunate consequence that buffer allocation is more likely to fail. It also no longer uses the `__GFP_COMP` flag when allocating DMA coherent memory, no longer marks the allocated pages of DMA coherent memory as reserved, and no longer vmap's the DMA coherent memory pages (since they are contiguous anyway). Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-06-25 12:26:59 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: fix circular locking dependency in comedi_mmap() Mmapping a comedi data buffer with lockdep checking enabled produced the following kernel debug messages: ====================================================== [ INFO: possible circular locking dependency detected ] 3.5.0-rc3-ija1+ #9 Tainted: G C ------------------------------------------------------- comedi_test/4160 is trying to acquire lock: (&dev->mutex#2){+.+.+.}, at: [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] but task is already holding lock: (&mm->mmap_sem){++++++}, at: [<ffffffff810c96fe>] vm_mmap_pgoff+0x41/0x76 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++++}: [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff810ce3bc>] might_fault+0x6d/0x90 [<ffffffffa0031ffb>] do_devinfo_ioctl.isra.7+0x11e/0x14c [comedi] [<ffffffffa003227f>] comedi_unlocked_ioctl+0x256/0xe48 [comedi] [<ffffffff810f7fcd>] vfs_ioctl+0x18/0x34 [<ffffffff810f87fd>] do_vfs_ioctl+0x382/0x43c [<ffffffff810f88f9>] sys_ioctl+0x42/0x65 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b -> #0 (&dev->mutex#2){+.+.+.}: [<ffffffff8106c528>] __lock_acquire+0x101d/0x1591 [<ffffffff8106d0e8>] lock_acquire+0x97/0x105 [<ffffffff8140c894>] mutex_lock_nested+0x46/0x2a4 [<ffffffffa00313f4>] comedi_mmap+0x57/0x1d9 [comedi] [<ffffffff810d5816>] mmap_region+0x281/0x492 [<ffffffff810d5c92>] do_mmap_pgoff+0x26b/0x2a7 [<ffffffff810c971a>] vm_mmap_pgoff+0x5d/0x76 [<ffffffff810d493f>] sys_mmap_pgoff+0xc7/0x10d [<ffffffff81004d36>] sys_mmap+0x16/0x20 [<ffffffff81415c62>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(&dev->mutex#2); lock(&mm->mmap_sem); lock(&dev->mutex#2); *** DEADLOCK *** To avoid the circular dependency, just try to get the lock in `comedi_mmap()` instead of blocking. Since the comedi device's main mutex is heavily used, do a down-read of its `attach_lock` rwsemaphore instead. Trying to down-read `attach_lock` should only fail if some task has down-write locked it, and that is only done while the comedi device is being attached to or detached from a low-level hardware device. Unfortunately, acquiring the `attach_lock` doesn't prevent another task replacing the comedi data buffer we are trying to mmap. The details of the buffer are held in a `struct comedi_buf_map` and pointed to by `s->async->buf_map` where `s` is the comedi subdevice whose buffer we are trying to map. The `struct comedi_buf_map` is already reference counted with a `struct kref`, so we can stop it being freed prematurely. Modify `comedi_mmap()` to call new function `comedi_buf_map_from_subdev_get()` to read the subdevice's current buffer map pointer and increment its reference instead of accessing `async->buf_map` directly. Call `comedi_buf_map_put()` to decrement the reference once the buffer map structure has been dealt with. (Note that `comedi_buf_map_put()` does nothing if passed a NULL pointer.) `comedi_buf_map_from_subdev_get()` checks the subdevice's buffer map pointer has been set and the buffer map has been initialized enough for `comedi_mmap()` to deal with it (specifically, check the `n_pages` member has been set to a non-zero value). If all is well, the buffer map's reference is incremented and a pointer to it is returned. The comedi subdevice's spin-lock is used to protect the checks. Also use the spin-lock in `__comedi_buf_alloc()` and `__comedi_buf_free()` to protect changes to the subdevice's buffer map structure pointer and the buffer map structure's `n_pages` member. (This checking of `n_pages` is a bit clunky and I [Ian Abbott] plan to deal with it in the future.) Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Cc: <stable@vger.kernel.org> # 3.14.x, 3.15.x Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-10 19:41:57 +01:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00
staging: comedi: protect buffer from being freed while mmapped If a comedi device is automatically detached by `comedi_auto_unconfig()` any data buffers associated with subdevices that support asynchronous commands will be freed. If the buffer is mmapped at the time, bad things are likely to happen! Prevent this by moving some of the buffer details from `struct comedi_async` into a new, dynamically allocated, and kref-counted `struct comedi_buf_map`. This holds a list of pages, a reference count, and enough information to free the pages. The new member `buf_map` of `struct comedi_async` points to a `struct comedi_buf_map` when the buffer size is non-zero. Provide a new helper function `comedi_buf_is_mapped()` to check whether an a buffer is mmapped. If it is mmapped, the buffer is not allowed to be resized and the device is not allowed to be manually detached by the `COMEDI_DEVCONFIG` ioctl. Provide helper functions `comedi_buf_map_get()` and `comedi_buf_map_put()` to manipulate the reference count of the `struct comedi_buf_map`, which will be freed along with its contents via the 'release' callback of the `kref_put()` call. The reference count is manipulated by the vma operations and the mmap file operation. Now, when the comedi device is automatically detached, the buffer will be effectively freed by calling `comedi_buf_alloc()` with a new buffer size of 0. That calls local function `__comedi_buf_free()` which calls `comedi_buf_map_put()` on the `buf_map` member to free it. It won't actually be freed until the final 'put'. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-11-08 15:03:43 +00:00