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auxdisplay: charlcd: properly restore atomic counter on error path

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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. ]

Fixes: f4757af85 # 3.19-rc1
Cc: stable@vger.kernel.org
Cc: Mariusz Gorski <marius.gorski@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Miguel Ojeda Sandonis <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Willy Tarreau 2017-09-07 15:37:30 +02:00 committed by Greg Kroah-Hartman
parent d53bebdf4d
commit 93dc1774d2
2 changed files with 19 additions and 5 deletions
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11
drivers/auxdisplay/charlcd.c
View File

@ -647,18 +647,25 @@ static ssize_t charlcd_write(struct file *file, const char __user *buf,
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)

13
drivers/auxdisplay/panel.c
View File

@ -1105,14 +1105,21 @@ static ssize_t keypad_read(struct file *file,
static int keypad_open(struct inode *inode, struct file *file)
{
if (!atomic_dec_and_test(&keypad_available))
return -EBUSY; /* open only once at a time */
int ret;
ret = -EBUSY;
if (!atomic_dec_and_test(&keypad_available))
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)