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loop: set PF_MEMALLOC_NOIO for the worker thread
A deadlock with this stacktrace was observed. The loop thread does a GFP_KERNEL allocation, it calls into dm-bufio shrinker and the shrinker depends on I/O completion in the dm-bufio subsystem. In order to fix the deadlock (and other similar ones), we set the flag PF_MEMALLOC_NOIO at loop thread entry. PID: 474 TASK: ffff8813e11f4600 CPU: 10 COMMAND: "kswapd0" #0 [ffff8813dedfb938] __schedule at ffffffff8173f405 MiCode#1 [ffff8813dedfb990] schedule at ffffffff8173fa27 MiCode#2 [ffff8813dedfb9b0] schedule_timeout at ffffffff81742fec MiCode#3 [ffff8813dedfba60] io_schedule_timeout at ffffffff8173f186 MiCode#4 [ffff8813dedfbaa0] bit_wait_io at ffffffff8174034f MiCode#5 [ffff8813dedfbac0] __wait_on_bit at ffffffff8173fec8 MiCode#6 [ffff8813dedfbb10] out_of_line_wait_on_bit at ffffffff8173ff81 MiCode#7 [ffff8813dedfbb90] __make_buffer_clean at ffffffffa038736f [dm_bufio] MiCode#8 [ffff8813dedfbbb0] __try_evict_buffer at ffffffffa0387bb8 [dm_bufio] MiCode#9 [ffff8813dedfbbd0] dm_bufio_shrink_scan at ffffffffa0387cc3 [dm_bufio] MiCode#10 [ffff8813dedfbc40] shrink_slab at ffffffff811a87ce MiCode#11 [ffff8813dedfbd30] shrink_zone at ffffffff811ad778 MiCode#12 [ffff8813dedfbdc0] kswapd at ffffffff811ae92f MiCode#13 [ffff8813dedfbec0] kthread at ffffffff810a8428 MiCode#14 [ffff8813dedfbf50] ret_from_fork at ffffffff81745242 PID: 14127 TASK: ffff881455749c00 CPU: 11 COMMAND: "loop1" #0 [ffff88272f5af228] __schedule at ffffffff8173f405 MiCode#1 [ffff88272f5af280] schedule at ffffffff8173fa27 MiCode#2 [ffff88272f5af2a0] schedule_preempt_disabled at ffffffff8173fd5e MiCode#3 [ffff88272f5af2b0] __mutex_lock_slowpath at ffffffff81741fb5 MiCode#4 [ffff88272f5af330] mutex_lock at ffffffff81742133 MiCode#5 [ffff88272f5af350] dm_bufio_shrink_count at ffffffffa03865f9 [dm_bufio] MiCode#6 [ffff88272f5af380] shrink_slab at ffffffff811a86bd MiCode#7 [ffff88272f5af470] shrink_zone at ffffffff811ad778 MiCode#8 [ffff88272f5af500] do_try_to_free_pages at ffffffff811adb34 MiCode#9 [ffff88272f5af590] try_to_free_pages at ffffffff811adef8 MiCode#10 [ffff88272f5af610] __alloc_pages_nodemask at ffffffff811a09c3 MiCode#11 [ffff88272f5af710] alloc_pages_current at ffffffff811e8b71 MiCode#12 [ffff88272f5af760] new_slab at ffffffff811f4523 MiCode#13 [ffff88272f5af7b0] __slab_alloc at ffffffff8173a1b5 MiCode#14 [ffff88272f5af880] kmem_cache_alloc at ffffffff811f484b MiCode#15 [ffff88272f5af8d0] do_blockdev_direct_IO at ffffffff812535b3 MiCode#16 [ffff88272f5afb00] __blockdev_direct_IO at ffffffff81255dc3 MiCode#17 [ffff88272f5afb30] xfs_vm_direct_IO at ffffffffa01fe3fc [xfs] MiCode#18 [ffff88272f5afb90] generic_file_read_iter at ffffffff81198994 MiCode#19 [ffff88272f5afc50] __dta_xfs_file_read_iter_2398 at ffffffffa020c970 [xfs] MiCode#20 [ffff88272f5afcc0] lo_rw_aio at ffffffffa0377042 [loop] MiCode#21 [ffff88272f5afd70] loop_queue_work at ffffffffa0377c3b [loop] MiCode#22 [ffff88272f5afe60] kthread_worker_fn at ffffffff810a8a0c MiCode#23 [ffff88272f5afec0] kthread at ffffffff810a8428 MiCode#24 [ffff88272f5aff50] ret_from_fork at ffffffff81745242 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
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