linux-kernel - Re: [bug-report] task info hung problem in fb_deferred_io

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Date: Thu, 18 Apr 2024 21:29:57 +0200
From: Helge Deller <deller@....de>
To: Takashi Iwai <tiwai@...e.de>, Nam Cao <namcao@...utronix.de>,
 Thomas Zimmermann <tzimmermann@...e.de>
Cc: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
 Daniel Vetter <daniel@...ll.ch>, linux-fbdev@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, bigeasy@...utronix.de,
 patrik.r.jakobsson@...il.com, LKML <linux-kernel@...r.kernel.org>,
 Vegard Nossum <vegard.nossum@...cle.com>,
 George Kennedy <george.kennedy@...cle.com>,
 Darren Kenny <darren.kenny@...cle.com>, chuansheng.liu@...el.com
Subject: Re: [bug-report] task info hung problem in fb_deferred_io_work()

On 4/18/24 16:26, Takashi Iwai wrote:
> On Thu, 18 Apr 2024 16:06:52 +0200,
> Nam Cao wrote:
>>
>> On 2024-04-18 Harshit Mogalapalli wrote:
>>> While fuzzing 5.15.y kernel with Syzkaller, we noticed a INFO: task hung
>>> bug in fb_deferred_io_work()
>>
>> Which framebuffer device are you using exactly? It is possible that
>> the problem is with the device driver, not core framebuffer.
>
> Note that it was already known that using flush_delayed_work() caused
> a problem.  See the thread of the fix patch:
>    https://lore.kernel.org/all/20230129082856.22113-1-tiwai@suse.de/

Harshit reported the hung tasks with kernel v5.15-stable, and can even reproduce
that issue with kernel v6.9-rc4 although it has all of your patches from
that referenced mail thread applied.
So, what does your statement that "it was already known that it causes problems" exactly mean?
Can it be fixed? Is someone looking into fixing it?

> BTW, the problem is seen with bochs drm.

Helge