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Jason Gunthorpe 70df291bf8 mm/mmu_notifiers: do not speculatively allocate a mmu_notifier_mm 
A prior commit e0f3c3f78d ("mm/mmu_notifier: init notifier if necessary")
made an attempt at doing this, but had to be reverted as calling
the GFP_KERNEL allocator under the i_mmap_mutex causes deadlock, see
commit 35cfa2b0b4 ("mm/mmu_notifier: allocate mmu_notifier in advance").

However, we can avoid that problem by doing the allocation only under
the mmap_sem, which is already happening.

Since all writers to mm->mmu_notifier_mm hold the write side of the
mmap_sem reading it under that sem is deterministic and we can use that to
decide if the allocation path is required, without speculation.

The actual update to mmu_notifier_mm must still be done under the
mm_take_all_locks() to ensure read-side coherency.

Link: https://lore.kernel.org/r/20190806231548.25242-3-jgg@ziepe.ca
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
History 2019-08-16 11:44:48 -03:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.