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Subject[PATCH] block: fix a crash in do_task_dead()
Date
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;

Fix it by calling wake_up_process() if it is in a non-task context.

Fixes: 0619317ff8ba ("block: add polled wakeup task helper")
Signed-off-by: Qian Cai <cai@lca.pw>
---
include/linux/blkdev.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 592669bcc536..290eb7528f54 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1803,7 +1803,7 @@ static inline void blk_wake_io_task(struct task_struct *waiter)
* that case, we don't need to signal a wakeup, it's enough to just
* mark us as RUNNING.
*/
- if (waiter == current)
+ if (waiter == current && in_task())
__set_current_state(TASK_RUNNING);
else
wake_up_process(waiter);
--
1.8.3.1
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