From: Willy Tarreau <w@1wt.eu>
Date: Thu, 7 Sep 2017 09:56:40 +0000 (+0200)
Subject: misc: panel: properly restore atomic counter on error path
X-Git-Tag: archive/raspbian/4.9.80-2+rpi1~7^2~1312
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=e81b96cab11f57506ade92656a76db8bbe7b6673;p=linux-4.9.git

misc: panel: properly restore atomic counter on error path

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).

Fixes: f4757af85 # 3.19-rc1
Cc: Mariusz Gorski <marius.gorski@gmail.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
[wt: driver is in misc/panel in 4.9]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/misc/panel.c b/drivers/misc/panel.c
index 6030ac5b8c63..a9fa4c0ac220 100644
--- a/drivers/misc/panel.c
+++ b/drivers/misc/panel.c
@@ -1423,17 +1423,25 @@ static ssize_t lcd_write(struct file *file,
 
 static int lcd_open(struct inode *inode, struct file *file)
 {
+	int ret;
+
+	ret = -EBUSY;
 	if (!atomic_dec_and_test(&lcd_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 (lcd.must_clear) {
 		lcd_clear_display();
 		lcd.must_clear = false;
 	}
 	return nonseekable_open(inode, file);
+
+ fail:
+	atomic_inc(&lcd_available);
+	return ret;
 }
 
 static int lcd_release(struct inode *inode, struct file *file)
@@ -1696,14 +1704,21 @@ static ssize_t keypad_read(struct file *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)