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 staging/panel in 4.4]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/panel/panel.c b/drivers/staging/panel/panel.c
index 70b8f4f..e658e11 100644 (file)
--- a/drivers/staging/panel/panel.c
+++ b/drivers/staging/panel/panel.c
@@ -1431,17 +1431,25 @@ 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)
@@ -1704,14 +1712,21 @@ 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)