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?
> Fixes: 0619317ff8ba ("block: add polled wakeup task helper")
That will be needing a cc:stable, no?
> ...
>
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -140,7 +140,8 @@ static void end_swap_bio_read(struct bio *bio)
> unlock_page(page);
> WRITE_ONCE(bio->bi_private, NULL);
> bio_put(bio);
> - blk_wake_io_task(waiter);
> + /* end_swap_bio_read() could be called from an interrupt handler. */
> + wake_up_process(waiter);
> put_task_struct(waiter);
> }
