On 5/29/19 4:44 PM, Andrew Morton wrote:
> On Wed, 29 May 2019 15:06:53 -0400 Qian Cai <cai@xxxxxx> 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
