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Subject: Re: [PATCH] mm/page_io: fix a crash in do_task_dead()
To:     Andrew Morton <akpm@linux-foundation.org>, Qian Cai <cai@lca.pw>
Cc:     hch@lst.de, peterz@infradead.org, oleg@redhat.com,
        gkohli@codeaurora.org, mingo@redhat.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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 <20190529154424.c0fe2758cf5af42ff258714a@linux-foundation.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <73a24780-6760-926b-40be-7a31562704d8@kernel.dk>
Date:   Wed, 29 May 2019 16:57:11 -0600
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On 5/29/19 4:44 PM, Andrew Morton wrote:
> On Wed, 29 May 2019 15:06:53 -0400 Qian Cai <cai@lca.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