[PATCH v3 1/1] v4l: event: Add subscription to list before calling "add" operation

[PATCH v3 1/1] v4l: event: Add subscription to list before calling "add" operation

[Sakari Ailus]

Patch ad608fbcf166 changed how events were subscribed to address an issue
elsewhere. As a side effect of that change, the "add" callback was called
before the event subscription was added to the list of subscribed events,
causing the first event queued by the add callback (and possibly other
events arriving soon afterwards) to be lost.

Fix this by adding the subscription to the list before calling the "add"
callback, and clean up afterwards if that fails.

Fixes: ad608fbcf166 ("media: v4l: event: Prevent freeing event subscriptions while accessed")

Reported-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
since v2:

- More accurate commit message. No other changes.

 drivers/media/v4l2-core/v4l2-event.c | 43 ++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c
index a3ef1f50a4b3..481e3c65cf97 100644
--- a/drivers/media/v4l2-core/v4l2-event.c
+++ b/drivers/media/v4l2-core/v4l2-event.c
@@ -193,6 +193,22 @@ int v4l2_event_pending(struct v4l2_fh *fh)
 }
 EXPORT_SYMBOL_GPL(v4l2_event_pending);
 
+static void __v4l2_event_unsubscribe(struct v4l2_subscribed_event *sev)
+{
+	struct v4l2_fh *fh = sev->fh;
+	unsigned int i;
+
+	lockdep_assert_held(&fh->subscribe_lock);
+	assert_spin_locked(&fh->vdev->fh_lock);
+
+	/* Remove any pending events for this subscription */
+	for (i = 0; i < sev->in_use; i++) {
+		list_del(&sev->events[sev_pos(sev, i)].list);
+		fh->navailable--;
+	}
+	list_del(&sev->list);
+}
+
 int v4l2_event_subscribe(struct v4l2_fh *fh,
 			 const struct v4l2_event_subscription *sub, unsigned elems,
 			 const struct v4l2_subscribed_event_ops *ops)
@@ -224,27 +240,23 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
 
 	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
 	found_ev = v4l2_event_subscribed(fh, sub->type, sub->id);
+	if (!found_ev)
+		list_add(&sev->list, &fh->subscribed);
 	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
 
 	if (found_ev) {
 		/* Already listening */
 		kvfree(sev);
-		goto out_unlock;
-	}
-
-	if (sev->ops && sev->ops->add) {
+	} else if (sev->ops && sev->ops->add) {
 		ret = sev->ops->add(sev, elems);
 		if (ret) {
+			spin_lock_irqsave(&fh->vdev->fh_lock, flags);
+			__v4l2_event_unsubscribe(sev);
+			spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
 			kvfree(sev);
-			goto out_unlock;
 		}
 	}
 
-	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
-	list_add(&sev->list, &fh->subscribed);
-	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
-
-out_unlock:
 	mutex_unlock(&fh->subscribe_lock);
 
 	return ret;
@@ -279,7 +291,6 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
 {
 	struct v4l2_subscribed_event *sev;
 	unsigned long flags;
-	int i;
 
 	if (sub->type == V4L2_EVENT_ALL) {
 		v4l2_event_unsubscribe_all(fh);
@@ -291,14 +302,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
 	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
 
 	sev = v4l2_event_subscribed(fh, sub->type, sub->id);
-	if (sev != NULL) {
-		/* Remove any pending events for this subscription */
-		for (i = 0; i < sev->in_use; i++) {
-			list_del(&sev->events[sev_pos(sev, i)].list);
-			fh->navailable--;
-		}
-		list_del(&sev->list);
-	}
+	if (sev != NULL)
+		__v4l2_event_unsubscribe(sev);
 
 	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
 
-- 
2.11.0

Re: [PATCH v3 1/1] v4l: event: Add subscription to list before calling "add" operation

[Hans Verkuil]

On 11/06/2018 09:00 AM, Sakari Ailus wrote:
> Patch ad608fbcf166 changed how events were subscribed to address an issue
> elsewhere. As a side effect of that change, the "add" callback was called
> before the event subscription was added to the list of subscribed events,
> causing the first event queued by the add callback (and possibly other
> events arriving soon afterwards) to be lost.
> 
> Fix this by adding the subscription to the list before calling the "add"
> callback, and clean up afterwards if that fails.
> 
> Fixes: ad608fbcf166 ("media: v4l: event: Prevent freeing event subscriptions while accessed")
> 
> Reported-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Tested-by: Hans Verkuil <hans.verkuil@cisco.com>

Tested with vivid & v4l2-compliance.

Regards,

	Hans

> ---
> since v2:
> 
> - More accurate commit message. No other changes.
> 
>  drivers/media/v4l2-core/v4l2-event.c | 43 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c
> index a3ef1f50a4b3..481e3c65cf97 100644
> --- a/drivers/media/v4l2-core/v4l2-event.c
> +++ b/drivers/media/v4l2-core/v4l2-event.c
> @@ -193,6 +193,22 @@ int v4l2_event_pending(struct v4l2_fh *fh)
>  }
>  EXPORT_SYMBOL_GPL(v4l2_event_pending);
>  
> +static void __v4l2_event_unsubscribe(struct v4l2_subscribed_event *sev)
> +{
> +	struct v4l2_fh *fh = sev->fh;
> +	unsigned int i;
> +
> +	lockdep_assert_held(&fh->subscribe_lock);
> +	assert_spin_locked(&fh->vdev->fh_lock);
> +
> +	/* Remove any pending events for this subscription */
> +	for (i = 0; i < sev->in_use; i++) {
> +		list_del(&sev->events[sev_pos(sev, i)].list);
> +		fh->navailable--;
> +	}
> +	list_del(&sev->list);
> +}
> +
>  int v4l2_event_subscribe(struct v4l2_fh *fh,
>  			 const struct v4l2_event_subscription *sub, unsigned elems,
>  			 const struct v4l2_subscribed_event_ops *ops)
> @@ -224,27 +240,23 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
>  
>  	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
>  	found_ev = v4l2_event_subscribed(fh, sub->type, sub->id);
> +	if (!found_ev)
> +		list_add(&sev->list, &fh->subscribed);
>  	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>  
>  	if (found_ev) {
>  		/* Already listening */
>  		kvfree(sev);
> -		goto out_unlock;
> -	}
> -
> -	if (sev->ops && sev->ops->add) {
> +	} else if (sev->ops && sev->ops->add) {
>  		ret = sev->ops->add(sev, elems);
>  		if (ret) {
> +			spin_lock_irqsave(&fh->vdev->fh_lock, flags);
> +			__v4l2_event_unsubscribe(sev);
> +			spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>  			kvfree(sev);
> -			goto out_unlock;
>  		}
>  	}
>  
> -	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
> -	list_add(&sev->list, &fh->subscribed);
> -	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
> -
> -out_unlock:
>  	mutex_unlock(&fh->subscribe_lock);
>  
>  	return ret;
> @@ -279,7 +291,6 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
>  {
>  	struct v4l2_subscribed_event *sev;
>  	unsigned long flags;
> -	int i;
>  
>  	if (sub->type == V4L2_EVENT_ALL) {
>  		v4l2_event_unsubscribe_all(fh);
> @@ -291,14 +302,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
>  	spin_lock_irqsave(&fh->vdev->fh_lock, flags);
>  
>  	sev = v4l2_event_subscribed(fh, sub->type, sub->id);
> -	if (sev != NULL) {
> -		/* Remove any pending events for this subscription */
> -		for (i = 0; i < sev->in_use; i++) {
> -			list_del(&sev->events[sev_pos(sev, i)].list);
> -			fh->navailable--;
> -		}
> -		list_del(&sev->list);
> -	}
> +	if (sev != NULL)
> +		__v4l2_event_unsubscribe(sev);
>  
>  	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>  
> 

Re: [PATCH v3 1/1] v4l: event: Add subscription to list before calling "add" operation

[Dave Stevenson]

On Tue, 6 Nov 2018 at 08:00, Sakari Ailus <sakari.ailus@linux.intel.com> wrote:
>
> Patch ad608fbcf166 changed how events were subscribed to address an issue
> elsewhere. As a side effect of that change, the "add" callback was called
> before the event subscription was added to the list of subscribed events,
> causing the first event queued by the add callback (and possibly other
> events arriving soon afterwards) to be lost.
>
> Fix this by adding the subscription to the list before calling the "add"
> callback, and clean up afterwards if that fails.
>
> Fixes: ad608fbcf166 ("media: v4l: event: Prevent freeing event subscriptions while accessed")
>
> Reported-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>

Tested-By: Dave Stevenson <dave.stevenson@raspberrypi.org>

Tested with 3 bcm2835 drivers (camera driver in staging, CSI2
receiver, and codec M2M driver) via v4l2-compliance on 4.19.0. All 3
failed in the same way prior to this patch.

> ---
> since v2:
>
> - More accurate commit message. No other changes.
>
>  drivers/media/v4l2-core/v4l2-event.c | 43 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c
> index a3ef1f50a4b3..481e3c65cf97 100644
> --- a/drivers/media/v4l2-core/v4l2-event.c
> +++ b/drivers/media/v4l2-core/v4l2-event.c
> @@ -193,6 +193,22 @@ int v4l2_event_pending(struct v4l2_fh *fh)
>  }
>  EXPORT_SYMBOL_GPL(v4l2_event_pending);
>
> +static void __v4l2_event_unsubscribe(struct v4l2_subscribed_event *sev)
> +{
> +       struct v4l2_fh *fh = sev->fh;
> +       unsigned int i;
> +
> +       lockdep_assert_held(&fh->subscribe_lock);
> +       assert_spin_locked(&fh->vdev->fh_lock);
> +
> +       /* Remove any pending events for this subscription */
> +       for (i = 0; i < sev->in_use; i++) {
> +               list_del(&sev->events[sev_pos(sev, i)].list);
> +               fh->navailable--;
> +       }
> +       list_del(&sev->list);
> +}
> +
>  int v4l2_event_subscribe(struct v4l2_fh *fh,
>                          const struct v4l2_event_subscription *sub, unsigned elems,
>                          const struct v4l2_subscribed_event_ops *ops)
> @@ -224,27 +240,23 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
>
>         spin_lock_irqsave(&fh->vdev->fh_lock, flags);
>         found_ev = v4l2_event_subscribed(fh, sub->type, sub->id);
> +       if (!found_ev)
> +               list_add(&sev->list, &fh->subscribed);
>         spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>
>         if (found_ev) {
>                 /* Already listening */
>                 kvfree(sev);
> -               goto out_unlock;
> -       }
> -
> -       if (sev->ops && sev->ops->add) {
> +       } else if (sev->ops && sev->ops->add) {
>                 ret = sev->ops->add(sev, elems);
>                 if (ret) {
> +                       spin_lock_irqsave(&fh->vdev->fh_lock, flags);
> +                       __v4l2_event_unsubscribe(sev);
> +                       spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>                         kvfree(sev);
> -                       goto out_unlock;
>                 }
>         }
>
> -       spin_lock_irqsave(&fh->vdev->fh_lock, flags);
> -       list_add(&sev->list, &fh->subscribed);
> -       spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
> -
> -out_unlock:
>         mutex_unlock(&fh->subscribe_lock);
>
>         return ret;
> @@ -279,7 +291,6 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
>  {
>         struct v4l2_subscribed_event *sev;
>         unsigned long flags;
> -       int i;
>
>         if (sub->type == V4L2_EVENT_ALL) {
>                 v4l2_event_unsubscribe_all(fh);
> @@ -291,14 +302,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
>         spin_lock_irqsave(&fh->vdev->fh_lock, flags);
>
>         sev = v4l2_event_subscribed(fh, sub->type, sub->id);
> -       if (sev != NULL) {
> -               /* Remove any pending events for this subscription */
> -               for (i = 0; i < sev->in_use; i++) {
> -                       list_del(&sev->events[sev_pos(sev, i)].list);
> -                       fh->navailable--;
> -               }
> -               list_del(&sev->list);
> -       }
> +       if (sev != NULL)
> +               __v4l2_event_unsubscribe(sev);
>
>         spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>
> --
> 2.11.0
>