[PATCH 2.6.32 18/38] [PATCH 18/38] Input: evdev - do not report errors form flush()

[Willy Tarreau <w@1wt.eu>]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

commit eb38f3a4f6e86f8bb10a3217ebd85ecc5d763aae upstream.

We've got bug reports showing the old systemd-logind (at least
system-210) aborting unexpectedly, and this turned out to be because
of an invalid error code from close() call to evdev devices.  close()
is supposed to return only either EINTR or EBADFD, while the device
returned ENODEV.  logind was overreacting to it and decided to kill
itself when an unexpected error code was received.  What a tragedy.

The bad error code comes from flush fops, and actually evdev_flush()
returns ENODEV when device is disconnected or client's access to it is
revoked. But in these cases the fact that flush did not actually happen is
not an error, but rather normal behavior. For non-disconnected devices
result of flush is also not that interesting as there is no potential of
data loss and even if it fails application has no way of handling the
error. Because of that we are better off always returning success from
evdev_flush().

Also returning EINTR from flush()/close() is discouraged (as it is not
clear how application should handle this error), so let's stop taking
evdev->mutex interruptibly.

Bugzilla: http://bugzilla.suse.com/show_bug.cgi?id=939834
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[bwh: Backported to 3.2: there's no revoked flag to test]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit a6706174cfe9fa100651b5012aec9796006a884b)

Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 drivers/input/evdev.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index dee6706..f05566f 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -102,19 +102,14 @@ static int evdev_flush(struct file *file, fl_owner_t id)
 {
 	struct evdev_client *client = file->private_data;
 	struct evdev *evdev = client->evdev;
-	int retval;
 
-	retval = mutex_lock_interruptible(&evdev->mutex);
-	if (retval)
-		return retval;
+	mutex_lock(&evdev->mutex);
 
-	if (!evdev->exist)
-		retval = -ENODEV;
-	else
-		retval = input_flush_device(&evdev->handle, file);
+	if (evdev->exist)
+		input_flush_device(&evdev->handle, file);
 
 	mutex_unlock(&evdev->mutex);
-	return retval;
+	return 0;
 }
 
 static void evdev_free(struct device *dev)
-- 
1.7.12.2.21.g234cd45.dirty