linux-kernel - Re: [PATCH 1/2] fb: flush deferred work in fb_deferred_io

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Message-ID: <4dd7ec87-eceb-4015-a0a0-45f6f0c12e9d@gmx.de>
Date: Tue, 19 Dec 2023 08:43:25 +0100
From: Helge Deller <deller@....de>
To: Nam Cao <namcao@...utronix.de>, Daniel Vetter <daniel@...ll.ch>,
 Antonino Daplas <adaplas@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Paul Mundt <lethal@...ux-sh.org>,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Cc: bigeasy@...utronix.de, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] fb: flush deferred work in fb_deferred_io_fsync()

On 12/18/23 10:57, Nam Cao wrote:
> The driver's fsync() is supposed to flush any pending operation to
> hardware. It is implemented in this driver by cancelling the queued
> deferred IO first, then schedule it for "immediate execution" by calling
> schedule_delayed_work() again with delay=0. However, setting delay=0
> only means the work is scheduled immediately, it does not mean the work
> is executed immediately. There is no guarantee that the work is finished
> after schedule_delayed_work() returns. After this driver's fsync()
> returns, there can still be pending work. Furthermore, if close() is
> called by users immediately after fsync(), the pending work gets
> cancelled and fsync() may do nothing.
>
> To ensure that the deferred IO completes, use flush_delayed_work()
> instead. Write operations to this driver either write to the device
> directly, or invoke schedule_delayed_work(); so by flushing the
> workqueue, it can be guaranteed that all previous writes make it to the
> device.
>
> Fixes: 5e841b88d23d ("fb: fsync() method for deferred I/O flush.")
> Cc: stable@...r.kernel.org
> Signed-off-by: Nam Cao <namcao@...utronix.de>
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>   drivers/video/fbdev/core/fb_defio.c | 6 +-----
>   1 file changed, 1 insertion(+), 5 deletions(-)

both patches applied to fbdev for-next git tree.

Thanks!
Helge