From 93dc1774d2a4c7a298d5cdf78cc8acdcb7b1428d Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Thu, 7 Sep 2017 15:37:30 +0200 Subject: [PATCH] auxdisplay: charlcd: properly restore atomic counter on error path 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 Cc: Geert Uytterhoeven Cc: Miguel Ojeda Sandonis Signed-off-by: Willy Tarreau Signed-off-by: Greg Kroah-Hartman --- drivers/auxdisplay/charlcd.c | 11 +++++++++-- drivers/auxdisplay/panel.c | 13 ++++++++++--- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c index cfeb049a01ef..642afd88870b 100644 --- a/drivers/auxdisplay/charlcd.c +++ b/drivers/auxdisplay/charlcd.c @@ -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) diff --git a/drivers/auxdisplay/panel.c b/drivers/auxdisplay/panel.c index df126dcdaf18..6911acd896d9 100644 --- a/drivers/auxdisplay/panel.c +++ b/drivers/auxdisplay/panel.c @@ -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)