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Date: Wed, 29 May 2019 16:57:11 -0600 From: Jens Axboe <axboe@...nel.dk> To: Andrew Morton <akpm@...ux-foundation.org>, Qian Cai <cai@....pw> Cc: hch@....de, peterz@...radead.org, oleg@...hat.com, gkohli@...eaurora.org, mingo@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] mm/page_io: fix a crash in do_task_dead() On 5/29/19 4:44 PM, Andrew Morton wrote: > On Wed, 29 May 2019 15:06:53 -0400 Qian Cai <cai@....pw> wrote: > >> The commit 0619317ff8ba ("block: add polled wakeup task helper") >> replaced wake_up_process() with blk_wake_io_task() in >> end_swap_bio_read() which triggers a crash when running heavy swapping >> workloads. >> >> [T114538] kernel BUG at kernel/sched/core.c:3462! >> [T114538] Process oom01 (pid: 114538, stack limit = 0x000000004f40e0c1) >> [T114538] Call trace: >> [T114538] do_task_dead+0xf0/0xf8 >> [T114538] do_exit+0xd5c/0x10fc >> [T114538] do_group_exit+0xf4/0x110 >> [T114538] get_signal+0x280/0xdd8 >> [T114538] do_notify_resume+0x720/0x968 >> [T114538] work_pending+0x8/0x10 >> >> This is because shortly after set_special_state(TASK_DEAD), >> end_swap_bio_read() is called from an interrupt handler that revive the >> task state to TASK_RUNNING causes __schedule() to return and trip the >> BUG() later. >> >> [ C206] Call trace: >> [ C206] dump_backtrace+0x0/0x268 >> [ C206] show_stack+0x20/0x2c >> [ C206] dump_stack+0xb4/0x108 >> [ C206] blk_wake_io_task+0x7c/0x80 >> [ C206] end_swap_bio_read+0x22c/0x31c >> [ C206] bio_endio+0x3d8/0x414 >> [ C206] dec_pending+0x280/0x378 [dm_mod] >> [ C206] clone_endio+0x128/0x2ac [dm_mod] >> [ C206] bio_endio+0x3d8/0x414 >> [ C206] blk_update_request+0x3ac/0x924 >> [ C206] scsi_end_request+0x54/0x350 >> [ C206] scsi_io_completion+0xf0/0x6f4 >> [ C206] scsi_finish_command+0x214/0x228 >> [ C206] scsi_softirq_done+0x170/0x1a4 >> [ C206] blk_done_softirq+0x100/0x194 >> [ C206] __do_softirq+0x350/0x790 >> [ C206] irq_exit+0x200/0x26c >> [ C206] handle_IPI+0x2e8/0x514 >> [ C206] gic_handle_irq+0x224/0x228 >> [ C206] el1_irq+0xb8/0x140 >> [ C206] _raw_spin_unlock_irqrestore+0x3c/0x74 >> [ C206] do_task_dead+0x88/0xf8 >> [ C206] do_exit+0xd5c/0x10fc >> [ C206] do_group_exit+0xf4/0x110 >> [ C206] get_signal+0x280/0xdd8 >> [ C206] do_notify_resume+0x720/0x968 >> [ C206] work_pending+0x8/0x10 >> >> Before the offensive commit, wake_up_process() will prevent this from >> happening by taking the pi_lock and bail out immediately if TASK_DEAD is >> set. >> >> if (!(p->state & TASK_NORMAL)) >> goto out; > > Nice description, thanks. > > And... ouch. blk_wake_io_task() is a scary thing - changing a task to > TASK_RUNNING state from interrupt context. I wonder whether the > assumptions which that is making hold true in all situations even after > this change. > > Is polled block IO important enough for doing this stuff? Andrew, you missed the improved patch, you were CC'ed on that one too and I queued it up a few hours ago: http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=6f3ead091fe2a8fb57a5996fe8b94237a896c6e9 Please drop this one. >> Fixes: 0619317ff8ba ("block: add polled wakeup task helper") > > That will be needing a cc:stable, no? Also added that when I did. -- Jens Axboe
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