Patch "auxdisplay: charlcd: properly restore atomic counter on error path" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

auxdisplay: charlcd: properly restore atomic counter on error path

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
auxdisplay-charlcd-properly-restore-atomic-counter-on-error-path.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Willy Tarreau <[email protected]>
Date: Thu, 7 Sep 2017 15:37:30 +0200
Subject: auxdisplay: charlcd: properly restore atomic counter on error path

From: Willy Tarreau <[email protected]>

commit 93dc1774d2a4c7a298d5cdf78cc8acdcb7b1428d upstream.

Commit f4757af ("staging: panel: Fix single-open policy race condition") introduced in 3.19-rc1 attempted to fix a race condition on the open, but failed to properly do it and used to exit without restoring the semaphore.

This results in -EBUSY being returned after the first open error until the module is reloaded or the system restarted (ie: consecutive to a dual open resulting in -EBUSY or to a permission error).

[ Note for stable maintainers: the code moved from drivers/misc/panel.c
to drivers/auxdisplay/{charlcd,panel}.c during 4.12. The patch easily applies there (modulo the renamed atomic counter) but I can provide a tested backport if desired. ]

---
 drivers/auxdisplay/charlcd.c |   11 +++++++++--
 drivers/auxdisplay/panel.c   |   11 +++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

@@ -647,18 +647,25 @@ static ssize_t charlcd_write(struct file
 static int charlcd_open(struct inode *inode, struct file *file)
 {
 	struct charlcd_priv *priv = to_priv(the_charlcd);
+	int ret;
 
+	ret = -EBUSY;
 	if (!atomic_dec_and_test(&charlcd_available))
-		return -EBUSY;	/* open only once at a time */
+		goto fail;	/* open only once at a time */
 
+	ret = -EPERM;
 	if (file->f_mode & FMODE_READ)	/* device is write-only */
-		return -EPERM;
+		goto fail;
 
 	if (priv->must_clear) {
 		charlcd_clear_display(&priv->lcd);
 		priv->must_clear = false;
 	}
 	return nonseekable_open(inode, file);
+
+ fail:
+	atomic_inc(&charlcd_available);
+	return ret;
 }
 
 static int charlcd_release(struct inode *inode, struct file *file)

@@ -1105,14 +1105,21 @@ static ssize_t keypad_read(struct file *
 
 static int keypad_open(struct inode *inode, struct file *file)
 {
+	int ret;
+
+	ret = -EBUSY;
 	if (!atomic_dec_and_test(&keypad_available))
-		return -EBUSY;	/* open only once at a time */
+		goto fail;	/* open only once at a time */
 
+	ret = -EPERM;
 	if (file->f_mode & FMODE_WRITE)	/* device is read-only */
-		return -EPERM;
+		goto fail;
 
 	keypad_buflen = 0;	/* flush the buffer on opening */
 	return 0;
+ fail:
+	atomic_inc(&keypad_available);
+	return ret;
 }
 
 static int keypad_release(struct inode *inode, struct file *file)

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/auxdisplay-charlcd-properly-restore-atomic-counter-on-error-path.patch