From: Tejun Heo <tj@kernel.org>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
linux-rpi-kernel <linux-rpi-kernel@lists.infradead.org>,
Bart Van Assche <bvanassche@acm.org>,
jgg@ziepe.ca, linux-kernel@vger.kernel.org,
Lai Jiangshan <jiangshanlai@gmail.com>,
Haakon Bugge <haakon.bugge@oracle.com>,
DRI mailing list <dri-devel@lists.freedesktop.org>,
Nicolas Saenz Julienne <nsaenz@kernel.org>
Subject: Re: [PATCH v2] workqueue: Warn flush attempt using system-wide workqueues
Date: Wed, 23 Feb 2022 11:35:35 -1000 [thread overview]
Message-ID: <Yhaop3T53bHo7v2I@slm.duckdns.org> (raw)
In-Reply-To: <4e5fe60d-abbb-6e73-b8cc-c3e1a314fbce@samsung.com>
On Wed, Feb 23, 2022 at 10:20:47PM +0100, Marek Szyprowski wrote:
> Hi All,
>
> On 17.02.2022 12:22, Tetsuo Handa wrote:
> > syzbot found a circular locking dependency which is caused by flushing
> > system_long_wq WQ [1]. Tejun Heo commented that it makes no sense at all
> > to call flush_workqueue() on the shared workqueues as the caller has no
> > idea what it's gonna end up waiting for.
> >
> > Although there is flush_scheduled_work() which flushes system_wq WQ with
> > "Think twice before calling this function! It's very easy to get into
> > trouble if you don't take great care." warning message, it will be too
> > difficult to guarantee that all users safely flush system-wide WQs.
> >
> > Therefore, let's change the direction to that developers had better use
> > their own WQs if flushing is inevitable. To give developers time to update
> > their modules, for now just emit a warning message when flush_workqueue()
> > or flush_work() is called on system-wide WQs. We will eventually convert
> > this warning message into WARN_ON() and kill flush_scheduled_work().
> >
> > Link: https://syzkaller.appspot.com/bug?extid=831661966588c802aae9 [1]
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>
> This patch landed in linux next-20220222 as commit 4a6a0ce060e4
> ("workqueue: Warn flush attempt using system-wide workqueues"). As it
> might be expected it exposed some calls to flush work. However it also
> causes boot failure of the Raspberry Pi 3 and 4 boards (kernel compiled
> from arm64/defconfig). In the log I see one call from the
> deferred_probe_initcall(), but it isn't critical for the boot process.
> The deadlock occurs when DRM registers emulated framebuffer on RPi4.
> RPi3 boots a bit further, to the shell prompt, but then the console is
> freezed. Reverting this patch on top of linux-next 'fixes' the boot.
Tetsuo, can you please revert the patch? The patch is incorrect in that it's
triggering also on work item flushes, not just workqueue flushes.
Thanks.
--
tejun
next prev parent reply other threads:[~2022-02-23 21:35 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-10 19:27 [syzbot] possible deadlock in worker_thread syzbot
2022-02-11 18:59 ` Bart Van Assche
2022-02-12 5:31 ` Tetsuo Handa
2022-02-12 16:37 ` Bart Van Assche
2022-02-12 17:14 ` Tetsuo Handa
2022-02-13 15:33 ` Leon Romanovsky
2022-02-13 23:06 ` Bart Van Assche
2022-02-14 1:08 ` Tetsuo Handa
2022-02-14 3:44 ` Tejun Heo
2022-02-14 13:36 ` Tetsuo Handa
2022-02-14 17:34 ` Tejun Heo
2022-02-15 10:26 ` Tetsuo Handa
2022-02-15 10:43 ` Haakon Bugge
2022-02-15 12:48 ` Tetsuo Handa
2022-02-15 17:05 ` Bart Van Assche
2022-02-15 22:05 ` Tetsuo Handa
2022-02-22 18:26 ` Tejun Heo
2022-02-17 11:22 ` [PATCH v2] workqueue: Warn flush attempt using system-wide workqueues Tetsuo Handa
2022-02-22 18:36 ` Tejun Heo
[not found] ` <CGME20220223212048eucas1p1fab5e35ff398eff57808a8f1125dd15f@eucas1p1.samsung.com>
2022-02-23 21:20 ` Marek Szyprowski
2022-02-23 21:35 ` Tejun Heo [this message]
2022-02-23 22:06 ` Tetsuo Handa
2022-02-17 12:27 ` [syzbot] possible deadlock in worker_thread Fabio M. De Francesco
2022-02-22 18:30 ` Tejun Heo
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