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[1/2] fb: flush deferred work in fb_deferred_io_fsync()

Message ID d15187348e7d7f76b7a1adf95aa5e3e3ecfc10b4.1702890493.git.namcao@linutronix.de
State New
Headers
Series fix LCD diplays sporadically not work |

Commit Message

Nam Cao Dec. 18, 2023, 9:57 a.m. UTC 
  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@vger.kernel.org
Signed-off-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/video/fbdev/core/fb_defio.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

Comments

Helge Deller Dec. 19, 2023, 7:43 a.m. UTC | #1 
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@vger.kernel.org
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.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
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index 274f5d0fa247..6c8b81c452f0 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -132,11 +132,7 @@  int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy
 		return 0;
 
 	inode_lock(inode);
-	/* Kill off the delayed work */
-	cancel_delayed_work_sync(&info->deferred_work);
-
-	/* Run it immediately */
-	schedule_delayed_work(&info->deferred_work, 0);
+	flush_delayed_work(&info->deferred_work);
 	inode_unlock(inode);
 
 	return 0;