The patch titled Subject: mm/page_io.c: fix a crash in do_task_dead() has been added to the -mm tree. Its filename is mm-page_io-fix-a-crash-in-do_task_dead.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-page_io-fix-a-crash-in-do_task_d... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_io-fix-a-crash-in-do_task_d...

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------------------------------------------------------ From: Qian Cai cai@lca.pw Subject: mm/page_io.c: fix a crash in do_task_dead()

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;

Link: http://lkml.kernel.org/r/1559156813-30681-1-git-send-email-cai@lca.pw Fixes: 0619317ff8ba ("block: add polled wakeup task helper") Signed-off-by: Qian Cai cai@lca.pw Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Jens Axboe axboe@kernel.dk Cc: Christoph Hellwig hch@lst.de Cc: Peter Zijlstra peterz@infradead.org Cc: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_io.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/page_io.c~mm-page_io-fix-a-crash-in-do_task_dead +++ a/mm/page_io.c @@ -140,7 +140,8 @@ out: 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); }

_

Patches currently in -mm which might be from cai@lca.pw are

iommu-intel-fix-variable-iommu-set-but-not-used.patch mm-page_io-fix-a-crash-in-do_task_dead.patch