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bb5ab77e85
Lockdep complains about possible circular locking dependencies when the i.MX SDMA driver issues console messages under its spinlock. While the SDMA driver calls back into the UART when issuing a message, the i.MX UART driver will never call back into the SDMA driver for this UART, because DMA is explicitly not used for UARTs providing the console. To avoid the lockdep warnings put the UART port lock for console devices into a separate subclass. This fixes possible deadlock warnings like the following which was provoked by adding a printk to the i.MX SDMA driver at a place where the driver holds its spinlock. ====================================================== WARNING: possible circular locking dependency detected 6.6.0-rc3-00045-g517852be693b-dirty #110 Not tainted ------------------------------------------------------ swapper/0/0 is trying to acquire lock: c1818e04 (console_owner){-...}-{0:0}, at: console_flush_all+0x1c4/0x634 but task is already holding lock: c44649e0 (&vc->lock){-...}-{3:3}, at: sdma_int_handler+0xc4/0x368 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&vc->lock){-...}-{3:3}: _raw_spin_lock_irqsave+0x4c/0x68 sdma_prep_dma_cyclic+0x1a8/0x21c imx_uart_startup+0x44c/0x5d4 uart_startup+0x120/0x2b0 uart_port_activate+0x44/0x98 tty_port_open+0x80/0xd0 uart_open+0x18/0x20 tty_open+0x120/0x664 chrdev_open+0xc0/0x214 do_dentry_open+0x1d0/0x544 path_openat+0xbb0/0xea0 do_filp_open+0x5c/0xd4 do_sys_openat2+0xb8/0xf0 sys_openat+0x8c/0xd8 ret_fast_syscall+0x0/0x1c -> #1 (&port_lock_key){-.-.}-{3:3}: _raw_spin_lock_irqsave+0x4c/0x68 imx_uart_console_write+0x164/0x1a0 console_flush_all+0x220/0x634 console_unlock+0x64/0x164 vprintk_emit+0xb0/0x390 vprintk_default+0x24/0x2c _printk+0x2c/0x5c register_console+0x244/0x478 serial_core_register_port+0x5c4/0x618 imx_uart_probe+0x4e0/0x7d4 platform_probe+0x58/0xb0 really_probe+0xc4/0x2e0 __driver_probe_device+0x84/0x1a0 driver_probe_device+0x2c/0x108 __driver_attach+0x94/0x17c bus_for_each_dev+0x7c/0xd0 bus_add_driver+0xc4/0x1cc driver_register+0x7c/0x114 imx_uart_init+0x20/0x40 do_one_initcall+0x7c/0x3c4 kernel_init_freeable+0x17c/0x228 kernel_init+0x14/0x140 ret_from_fork+0x14/0x24 -> #0 (console_owner){-...}-{0:0}: __lock_acquire+0x14b0/0x29a0 lock_acquire.part.0+0xb4/0x264 console_flush_all+0x20c/0x634 console_unlock+0x64/0x164 vprintk_emit+0xb0/0x390 vprintk_default+0x24/0x2c _printk+0x2c/0x5c sdma_int_handler+0xcc/0x368 __handle_irq_event_percpu+0x94/0x2d0 handle_irq_event+0x38/0xd0 handle_fasteoi_irq+0x98/0x248 handle_irq_desc+0x1c/0x2c gic_handle_irq+0x6c/0x90 generic_handle_arch_irq+0x2c/0x64 __irq_svc+0x90/0xbc cpuidle_enter_state+0x1a0/0x4f4 cpuidle_enter+0x30/0x40 do_idle+0x210/0x2b4 cpu_startup_entry+0x28/0x2c rest_init+0xd0/0x184 arch_post_acpi_subsys_init+0x0/0x8 other info that might help us debug this: Chain exists of: console_owner --> &port_lock_key --> &vc->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&vc->lock); lock(&port_lock_key); lock(&vc->lock); lock(console_owner); *** DEADLOCK *** 3 locks held by swapper/0/0: #0: c44649e0 (&vc->lock){-...}-{3:3}, at: sdma_int_handler+0xc4/0x368 #1: c1818d50 (console_lock){+.+.}-{0:0}, at: vprintk_default+0x24/0x2c #2: c1818d08 (console_srcu){....}-{0:0}, at: console_flush_all+0x44/0x634 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-rc3-00045-g517852be693b-dirty #110 Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) unwind_backtrace from show_stack+0x10/0x14 show_stack from dump_stack_lvl+0x60/0x90 dump_stack_lvl from check_noncircular+0x184/0x1b8 check_noncircular from __lock_acquire+0x14b0/0x29a0 __lock_acquire from lock_acquire.part.0+0xb4/0x264 lock_acquire.part.0 from console_flush_all+0x20c/0x634 console_flush_all from console_unlock+0x64/0x164 console_unlock from vprintk_emit+0xb0/0x390 vprintk_emit from vprintk_default+0x24/0x2c vprintk_default from _printk+0x2c/0x5c _printk from sdma_int_handler+0xcc/0x368 sdma_int_handler from __handle_irq_event_percpu+0x94/0x2d0 __handle_irq_event_percpu from handle_irq_event+0x38/0xd0 handle_irq_event from handle_fasteoi_irq+0x98/0x248 handle_fasteoi_irq from handle_irq_desc+0x1c/0x2c handle_irq_desc from gic_handle_irq+0x6c/0x90 gic_handle_irq from generic_handle_arch_irq+0x2c/0x64 generic_handle_arch_irq from __irq_svc+0x90/0xbc Exception stack(0xc1801ee8 to 0xc1801f30) 1ee0: ffffffff ffffffff 00000001 00030349 00000000 00000012 1f00: 00000000 d7e45f4b 00000012 00000000 d7e16d63 c1810828 00000000 c1801f38 1f20: c108125c c1081260 60010013 ffffffff __irq_svc from cpuidle_enter_state+0x1a0/0x4f4 cpuidle_enter_state from cpuidle_enter+0x30/0x40 cpuidle_enter from do_idle+0x210/0x2b4 do_idle from cpu_startup_entry+0x28/0x2c cpu_startup_entry from rest_init+0xd0/0x184 rest_init from arch_post_acpi_subsys_init+0x0/0x8 Reported-by: Tim van der Staaij <Tim.vanderstaaij@zigngroup.com> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> Link: https://lore.kernel.org/r/20230928064320.711603-1-s.hauer@pengutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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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.