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SubjectRe: [PATCH] dvb-core: Fix potential mutex_unlock without mutex_lock in dvb_dvr_read
On Thu, 23 Apr 2009 18:32:13 +0100
Simon Arlott <simon@fire.lp0.eu> wrote:

> dvb_dvr_read may unlock the dmxdev mutex and return -ENODEV,
> except this function is a file op and will never be called
> with the mutex held.
>
> There's existing mutex_lock and mutex_unlock around the actual
> read but it's commented out. These should probably be uncommented
> but the read blocks and this could block another non-blocking
> reader on the mutex instead.
>
> This change comments out the extra mutex_unlock.
>
> Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
> ---
> This has been on my TODO list for far too long... I did come
> up with a mutex_trylock/mutex_lock_interruptible version but
> claiming that it'll block when it may not doesn't make sense
> (and any blocking read would cause all non-blocking reads to
> continually return -EWOULDBLOCK until there is data).
>
> drivers/media/dvb/dvb-core/dmxdev.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/media/dvb/dvb-core/dmxdev.c b/drivers/media/dvb/dvb-core/dmxdev.c
> index c35fbb8..d6d098a 100644
> --- a/drivers/media/dvb/dvb-core/dmxdev.c
> +++ b/drivers/media/dvb/dvb-core/dmxdev.c
> @@ -247,7 +247,7 @@ static ssize_t dvb_dvr_read(struct file *file, char __user *buf, size_t count,
> int ret;
>
> if (dmxdev->exit) {
> - mutex_unlock(&dmxdev->mutex);
> + //mutex_unlock(&dmxdev->mutex);
> return -ENODEV;
> }

Is there any value in retaining all the commented-out lock operations,
or can we zap 'em?

--- a/drivers/media/dvb/dvb-core/dmxdev.c~dvb-core-fix-potential-mutex_unlock-without-mutex_lock-in-dvb_dvr_read-fix
+++ a/drivers/media/dvb/dvb-core/dmxdev.c
@@ -244,19 +244,13 @@ static ssize_t dvb_dvr_read(struct file
{
struct dvb_device *dvbdev = file->private_data;
struct dmxdev *dmxdev = dvbdev->priv;
- int ret;

- if (dmxdev->exit) {
- //mutex_unlock(&dmxdev->mutex);
+ if (dmxdev->exit)
return -ENODEV;
- }

- //mutex_lock(&dmxdev->mutex);
- ret = dvb_dmxdev_buffer_read(&dmxdev->dvr_buffer,
- file->f_flags & O_NONBLOCK,
- buf, count, ppos);
- //mutex_unlock(&dmxdev->mutex);
- return ret;
+ return dvb_dmxdev_buffer_read(&dmxdev->dvr_buffer,
+ file->f_flags & O_NONBLOCK,
+ buf, count, ppos);
}

static int dvb_dvr_set_buffer_size(struct dmxdev *dmxdev,
_


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