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(-)

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;