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Subject[PATCH 4.9 39/39] misc: panel: properly restore atomic counter on error path
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

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

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>
---
drivers/misc/panel.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)

--- a/drivers/misc/panel.c
+++ b/drivers/misc/panel.c
@@ -1423,17 +1423,25 @@ static ssize_t lcd_write(struct file *fi

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 *

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)

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