linux-kernel - Re: [PATCH] sched: Avoid that __wait_on_bit

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Date:	Tue, 9 Aug 2016 11:48:27 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Johannes Weiner" <hannes@...xchg.org>, Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

On 08/09/2016 10:15 AM, Oleg Nesterov wrote:
> On 08/08, Bart Van Assche wrote:
>>
>> No external modules were loaded when I triggered the lockup
> 
> Heh. Could you test the patch below?
> 
> Oleg.
> 
> --- x/kernel/sched/wait.c
> +++ x/kernel/sched/wait.c
> @@ -283,7 +283,7 @@ void abort_exclusive_wait(wait_queue_hea
>  	if (!list_empty(&wait->task_list))
>  		list_del_init(&wait->task_list);
>  	else if (waitqueue_active(q))
> -		__wake_up_locked_key(q, mode, key);
> +		__wake_up_locked_key(q, TASK_NORMAL, key);
>  	spin_unlock_irqrestore(&q->lock, flags);
>  }
>  EXPORT_SYMBOL(abort_exclusive_wait);

Hello Oleg,

That patch looks interesting to me. Unfortunately even with that patch
applied I still see lockups. These are the two lockups I have observed
after I had applied your patch, rebuilt and reinstalled the kernel and
rebooted the test server:

[ 1548.018115] sysrq: SysRq : Show Blocked State
[ 1548.018210]   task                        PC stack   pid father
[ 1548.018677] systemd-udevd   D ffff8803a9f13be8     0 29908    483 0x00000000
[ 1548.018792]  ffff8803a9f13be8 ffffffff82584bd0 00ffffff8252b1b0 ffff88046f0569c0
[ 1548.018961]  ffff88016c98b140 ffff8800757bc9c0 ffff8803a9f14000 ffff88046f0569c0
[ 1548.019131]  7fffffffffffffff ffffffff8161fcf0 ffff8803a9f13d50 ffff8803a9f13c00
[ 1548.019316] Call Trace:
[ 1548.019415]  [<ffffffff8161f567>] schedule+0x37/0x90
[ 1548.019464]  [<ffffffff81623bbf>] schedule_timeout+0x27f/0x470
[ 1548.019758]  [<ffffffff8161e93f>] io_schedule_timeout+0x9f/0x110
[ 1548.019808]  [<ffffffff8161fd06>] bit_wait_io+0x16/0x60
[ 1548.019856]  [<ffffffff8161f996>] __wait_on_bit+0x56/0x80
[ 1548.019906]  [<ffffffff81152e1d>] wait_on_page_bit_killable+0xbd/0xc0
[ 1548.020006]  [<ffffffff81152f50>] generic_file_read_iter+0x130/0x770
[ 1548.020158]  [<ffffffff812134a0>] blkdev_read_iter+0x30/0x40
[ 1548.020209]  [<ffffffff811d266b>] __vfs_read+0xbb/0x130
[ 1548.020258]  [<ffffffff811d2a51>] vfs_read+0x91/0x130
[ 1548.020305]  [<ffffffff811d3dd4>] SyS_read+0x44/0xa0
[ 1548.020354]  [<ffffffff81624fa5>] entry_SYSCALL_64_fastpath+0x18/0xa8

[ 1050.892823] sysrq: SysRq : Show Blocked State
[ 1050.892912]   task                        PC stack   pid father
[ 1050.893333] systemd-udevd   D ffff880449b3f838     0 17240    492 0x00000006
[ 1050.893974] Call Trace:
[ 1050.894119]  [<ffffffff8161f567>] schedule+0x37/0x90
[ 1050.894168]  [<ffffffff81623bcf>] schedule_timeout+0x27f/0x470
[ 1050.894561]  [<ffffffff8161e93f>] io_schedule_timeout+0x9f/0x110
[ 1050.894609]  [<ffffffff8161fd16>] bit_wait_io+0x16/0x60
[ 1050.894657]  [<ffffffff8161fb09>] __wait_on_bit_lock+0x49/0xa0
[ 1050.894705]  [<ffffffff8114fe59>] __lock_page+0xb9/0xc0
[ 1050.894802]  [<ffffffff81165d80>] truncate_inode_pages_range+0x3e0/0x760
[ 1050.895750]  [<ffffffff81166110>] truncate_inode_pages+0x10/0x20
[ 1050.895799]  [<ffffffff81212a10>] kill_bdev+0x30/0x40
[ 1050.895849]  [<ffffffff81213d31>] __blkdev_put+0x71/0x360
[ 1050.895951]  [<ffffffff81214069>] blkdev_put+0x49/0x170
[ 1050.895998]  [<ffffffff812141b0>] blkdev_close+0x20/0x30
[ 1050.896047]  [<ffffffff811d48d8>] __fput+0xe8/0x1f0
[ 1050.896094]  [<ffffffff811d4a19>] ____fput+0x9/0x10
[ 1050.896141]  [<ffffffff810842d3>] task_work_run+0x83/0xb0
[ 1050.896189]  [<ffffffff8106606e>] do_exit+0x3ee/0xc40
[ 1050.896284]  [<ffffffff8106694b>] do_group_exit+0x4b/0xc0
[ 1050.896331]  [<ffffffff81073d9a>] get_signal+0x2ca/0x940
[ 1050.896425]  [<ffffffff8101bf43>] do_signal+0x23/0x660
[ 1050.896626]  [<ffffffff810022b3>] exit_to_usermode_loop+0x73/0xb0
[ 1050.896678]  [<ffffffff81002cb0>] syscall_return_slowpath+0xb0/0xc0
[ 1050.896727]  [<ffffffff81625033>] entry_SYSCALL_64_fastpath+0xa6/0xa8

Bart.