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

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Date: Fri, 19 Apr 2024 17:34:43 +0200
From: Nam Cao <namcao@...utronix.de>
To: Patrik Jakobsson <patrik.r.jakobsson@...il.com>
Cc: Takashi Iwai <tiwai@...e.de>, Harshit Mogalapalli
 <harshit.m.mogalapalli@...cle.com>, Helge Deller <deller@....de>, Thomas
 Zimmermann <tzimmermann@...e.de>, Daniel Vetter <daniel@...ll.ch>,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 bigeasy@...utronix.de, 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 2024-04-19 Patrik Jakobsson wrote:
> Neither cancel_delayed_work_sync() or flush_delayed_work() prevent new
> work from being scheduled after they return.

flush_delayed_work() is called during device closing. And because no
writes are performed after the device has been closed, no new work
should be queued after flush_delayed_work().

> But
> cancel_delayed_work_sync() at least makes sure the queue is empty so
> the problem becomes less apparent.
> 
> Could this explain what we're seeing?

I suspect that cancel_delayed_work_sync() is only treating the symptoms
by preventing the deferred work from running. The real bug is "someone"
giving fb_deferred_io_work() invalid pages to work with. But that's
just a blind guess.

Best regards,
Nam