On 5/30/19 5:15 AM, Oleg Nesterov wrote:
> On 05/29, Qian Cai 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;
>
> I don't understand this code at all but I am just curious, can we do
> something like incomplete patch below ?
>
> Oleg.
>
> --- x/mm/page_io.c
> +++ x/mm/page_io.c
> @@ -140,8 +140,10 @@ int swap_readpage(struct page *page, bool synchronous)
> unlock_page(page);
> WRITE_ONCE(bio->bi_private, NULL);
> bio_put(bio);
> - blk_wake_io_task(waiter);
> - put_task_struct(waiter);
> + if (waiter) {
> + blk_wake_io_task(waiter);
> + put_task_struct(waiter);
> + }
> }
>
> int generic_swapfile_activate(struct swap_info_struct *sis,
> @@ -398,11 +400,12 @@ int swap_readpage(struct page *page, boo
> * Keep this task valid during swap readpage because the oom killer may
> * attempt to access it in the page fault retry time check.
> */
> - get_task_struct(current);
> - bio->bi_private = current;
> bio_set_op_attrs(bio, REQ_OP_READ, 0);
> - if (synchronous)
> + if (synchronous) {
> bio->bi_opf |= REQ_HIPRI;
> + get_task_struct(current);
> + bio->bi_private = current;
> + }
> count_vm_event(PSWPIN);
> bio_get(bio);
> qc = submit_bio(bio);
I think this would solve it for swap.
--
Jens Axboe
