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

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Date: Wed, 15 May 2024 22:12:00 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Sam Sun <samsun1006219@...il.com>
Cc: Hillf Danton <hdanton@...a.com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, axboe@...nel.dk,
        syzkaller-bugs@...glegroups.com, xrivendell7@...il.com
Subject: Re: [Linux kernel bug] INFO: task hung in blk_mq_get_tag

On 2024/05/15 21:46, Sam Sun wrote:
>> What happens if you disable
>>
>>   sysfd = write(sysfd, input, hash - input + 1);
>>
>> line (i.e. stop updating sg_allow_dio value) in the reproducer?
>>
> 
> I tried to change the value of /sys/module/sg/parameters/allow_dio to
> 0 and remove write() call, both still triggers task hang report and
> kernel panic. I think this write is not the call crashing the kernel.
> 

Kernel panic by general protection fault upon calling trigger_all_cpu_backtrace() is
a different bug. Please be sure to keep /proc/sys/kernel/hung_task_all_cpu_backtrace 0
while investigating this hung task problem.

This hung task problem happens without touching /sys/module/sg/parameters/allow_dio ,
doesn't it?

scsi_rescan_device() is reliably printed when this hung task problem happens,
isn't it?

Then, it is strange that scsi_rescan_device() is called despite the reproducer is
almost no-op. Maybe you can trigger scsi_rescan_device() without using the reproducer.

Can you simplify steps to reproduce? For example, doing a lot of write().