From: Nam Cao <namcao@linutronix.de>
To: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>,
jayalk@intworks.biz, Daniel Vetter <daniel@ffwll.ch>,
deller@gmx.de, linux-fbdev@vger.kernel.org,
dri-devel@lists.freedesktop.org, tiwai@suse.de,
bigeasy@linutronix.de, LKML <linux-kernel@vger.kernel.org>,
Vegard Nossum <vegard.nossum@oracle.com>,
George Kennedy <george.kennedy@oracle.com>,
Darren Kenny <darren.kenny@oracle.com>,
chuansheng.liu@intel.com
Subject: Re: [bug-report] task info hung problem in fb_deferred_io_work()
Date: Fri, 19 Apr 2024 17:18:35 +0200 [thread overview]
Message-ID: <20240419171835.5f31e32d@namcao> (raw)
In-Reply-To: <CAMeQTsaGXv6hUmXg3ROLb83JZEAfoSuQGCQgz0wG38Me8UtQYA@mail.gmail.com>
On 2024-04-18 Patrik Jakobsson wrote:
> On Thu, Apr 18, 2024 at 4:05 PM Nam Cao <namcao@linutronix.de> wrote:
> >
> > On 2024-04-18 Patrik Jakobsson wrote:
> > > This sounds similar to the SUSE bug [1]. We fixed it by reverting [2]
> > > in the SUSE kernel. The problem seems to be that flush_delayed_work()
> > > kills the timer and re-queues the work but doesn't guarantee that it
> > > is finished when returning. So when the device is closed, the
> > > fb_deferred_io_work() function can still be queued and tries to access
> > > memory that's been freed.
> >
> > flush_delayed_work() *does* guarantee the work is finished before
> > returning.
>
> Right, flush_work() does guarantee that the work is finished, but it
> doesn't guarantee that the queue is idle if work has been requeued
> since flush started. So fb_deferred_io_work() should be able to happen
> after the device is closed. Or am I missing something?
I'm confused: how is it possible for fb_deferred_io_work() to run after
the device is closed?
The workqueue is flushed during closing of device. If more work is
queued during/after the flushing, then someone must be writing to the
device during/after the closing of the device. How can that happen?
Best regards,
Nam
> >
> > > Patch [2] tries to solve the problem of not throwing away pending data
> > > when closing the device. Perhaps calling cancel_delayed_work_sync()
> > > and then follow up with a manual call to fb_deferred_io_work() would
> > > be enough to flush the remaining data?
> > >
> > > -Patrik
> > >
> > > [1] https://bugzilla.suse.com/show_bug.cgi?id=1221814
> > > [2] 33cd6ea9c067 fbdev: flush deferred IO before closing
> > >
> > > >
> > > >
> > > > Thanks,
> > > > Harshit
> >
next prev parent reply other threads:[~2024-04-19 15:18 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 12:39 [bug-report] task info hung problem in fb_deferred_io_work() Harshit Mogalapalli
2024-04-18 13:14 ` Patrik Jakobsson
2024-04-18 14:05 ` Nam Cao
2024-04-18 14:34 ` Patrik Jakobsson
2024-04-19 15:18 ` Nam Cao [this message]
2024-04-19 7:27 ` Harshit Mogalapalli
2024-04-18 14:06 ` Nam Cao
2024-04-18 14:26 ` Takashi Iwai
2024-04-18 19:29 ` Helge Deller
2024-04-19 6:44 ` Takashi Iwai
2024-04-19 7:39 ` Harshit Mogalapalli
2024-04-19 7:45 ` Takashi Iwai
2024-04-19 7:50 ` Patrik Jakobsson
2024-04-19 15:34 ` Nam Cao
2024-04-30 11:45 ` Patrik Jakobsson
2024-04-19 14:42 ` Harshit Mogalapalli
2024-04-19 7:35 ` Harshit Mogalapalli
2024-04-19 14:59 ` Nam Cao
2024-04-19 16:05 ` Harshit Mogalapalli
2024-04-19 16:23 ` Nam Cao
2024-04-19 16:39 ` Harshit Mogalapalli
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