V4L/DVB: IR/lirc_dev: fix locking in lirc_dev_fop_read

On Wed, Jul 07, 2010 at 02:52:58PM +0200, Jiri Slaby wrote:
> Hi,
>
> stanse found a locking error in lirc_dev_fop_read:
> if (mutex_lock_interruptible(&ir->irctl_lock))
>   return -ERESTARTSYS;
> ...
> while (written < length && ret == 0) {
>   if (mutex_lock_interruptible(&ir->irctl_lock)) {    #1
>     ret = -ERESTARTSYS;
>     break;
>   }
>   ...
> }
>
> remove_wait_queue(&ir->buf->wait_poll, &wait);
> set_current_state(TASK_RUNNING);
> mutex_unlock(&ir->irctl_lock);                        #2
>
> If lock at #1 fails, it beaks out of the loop, with the lock unlocked,
> but there is another "unlock" at #2.

This should do the trick. Completely untested beyond compiling, but its
not exactly a complicated fix, and in practice, I'm not aware of anyone
ever actually tripping that locking bug, so there's zero functional change
in typical use here.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/media/IR/lirc_dev.c b/drivers/media/IR/lirc_dev.c
index 9e141d51df91..64170fa58006 100644
--- a/drivers/media/IR/lirc_dev.c
+++ b/drivers/media/IR/lirc_dev.c
@@ -657,7 +657,9 @@ ssize_t lirc_dev_fop_read(struct file *file,
 
                         if (mutex_lock_interruptible(&ir->irctl_lock)) {
                                 ret = -ERESTARTSYS;
-                                break;
+                                remove_wait_queue(&ir->buf->wait_poll, &wait);
+                                set_current_state(TASK_RUNNING);
+                                goto out_unlocked;
                         }
 
                         if (!ir->attached) {
@@ -676,6 +678,7 @@ ssize_t lirc_dev_fop_read(struct file *file,
         set_current_state(TASK_RUNNING);
         mutex_unlock(&ir->irctl_lock);
 
+out_unlocked:
         dev_dbg(ir->d.dev, LOGHEAD "read result = %s (%d)\n",
                 ir->d.name, ir->d.minor, ret ? "-EFAULT" : "OK", ret);