linux-kernel - Re: [Linux kernel bug] INFO: task hung in blk_mq_get

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Date: Tue, 14 May 2024 10:05:21 +0800
From: Sam Sun <samsun1006219@...il.com>
To: Hillf Danton <hdanton@...a.com>
Cc: linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, axboe@...nel.dk, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, syzkaller-bugs@...glegroups.com, 
	xrivendell7@...il.com
Subject: Re: [Linux kernel bug] INFO: task hung in blk_mq_get_tag

On Tue, May 14, 2024 at 6:54 AM Hillf Danton <hdanton@...a.com> wrote:
>
> On Mon, 13 May 2024 20:57:44 +0800 Sam Sun <samsun1006219@...il.com>
> >
> > I applied this patch and tried using the C repro, but it still crashed
> > with the same task hang kernel dump log.
>
> Oh low-hanging pear is sour, and try again seeing if there is missing
> wakeup due to wake batch.
>
> --- x/lib/sbitmap.c
> +++ y/lib/sbitmap.c
> @@ -579,6 +579,8 @@ void sbitmap_queue_wake_up(struct sbitma
>         unsigned int wake_batch = READ_ONCE(sbq->wake_batch);
>         unsigned int wakeups;
>
> +       __sbitmap_queue_wake_up(sbq, nr);
> +
>         if (!atomic_read(&sbq->ws_active))
>                 return;
>
> --


I applied this patch together with the last patch. Unfortunately it
still crashed.

Pointed out by Tetsuo, this kernel panic might be caused by sending
NMI between cpus. As dump log shows:
```
[  429.046960][   T32] NMI backtrace for cpu 0
[  429.047499][   T32] CPU: 0 PID: 32 Comm: khungtaskd Not tainted
6.9.0-dirty #6
[  429.048417][   T32] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.org 04/01/2014
[  429.049873][   T32] Call Trace:
[  429.050299][   T32]  <TASK>
[  429.050672][   T32]  dump_stack_lvl+0x201/0x300
..
[  429.063133][   T32]  ret_from_fork_asm+0x11/0x20
[  429.063735][   T32]  </TASK>
[  429.064168][   T32] Sending NMI from CPU 0 to CPUs 1:
[  429.064833][   T32] BUG: unable to handle page fault for address:
ffffffff813d4cf1
[  429.065765][   T32] #PF: supervisor write access in kernel mode
[  429.066502][   T32] #PF: error_code(0x0003) - permissions violation
[  429.067274][   T32] PGD db38067 P4D db38067 PUD db39063 PMD 12001a1
[  429.068068][   T32] Oops: 0003 [#1] PREEMPT SMP KASAN NOPTI
[  429.068767][   T32] CPU: 0 PID: 32 Comm: khungtaskd Not tainted
6.9.0-dirty #6
[  429.069666][   T32] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS rel-1.16.1-0-g3208b098f51a-prebuilt.qemu.org 04/01/2014
[  429.071142][   T32] RIP: 0010:__send_ipi_mask+0x541/0x690
```
Should I add them to cc list?

Best,
Yue