V4L/DVB (13831): uvcvideo: Fix oops caused by a race condition in buffer dequeuing
Buffers were marked as done before being removed from the IRQ queue. If
a userspace application dequeued and requeued the buffer fast enough
during that time window, the buffer could end up being deleted twice,
generating an oops in interrupt context.
Add a new state, UVC_BUF_STATE_READY, to mark buffers as ready for reuse
but not yet removed from the queue, and transition to UVC_BUF_STATE_DONE
only when the buffer is removed from the queue.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/uvc/uvc_queue.c b/drivers/media/video/uvc/uvc_queue.c
index f854698..ea11839 100644
--- a/drivers/media/video/uvc/uvc_queue.c
+++ b/drivers/media/video/uvc/uvc_queue.c
@@ -59,9 +59,9 @@
* returns immediately.
*
* When the buffer is full, the completion handler removes it from the irq
- * queue, marks it as ready (UVC_BUF_STATE_DONE) and wakes its wait queue.
+ * queue, marks it as done (UVC_BUF_STATE_DONE) and wakes its wait queue.
* At that point, any process waiting on the buffer will be woken up. If a
- * process tries to dequeue a buffer after it has been marked ready, the
+ * process tries to dequeue a buffer after it has been marked done, the
* dequeing will succeed immediately.
*
* 2. Buffers are queued, user is waiting on a buffer and the device gets
@@ -201,6 +201,7 @@
break;
case UVC_BUF_STATE_QUEUED:
case UVC_BUF_STATE_ACTIVE:
+ case UVC_BUF_STATE_READY:
v4l2_buf->flags |= V4L2_BUF_FLAG_QUEUED;
break;
case UVC_BUF_STATE_IDLE:
@@ -295,13 +296,15 @@
{
if (nonblocking) {
return (buf->state != UVC_BUF_STATE_QUEUED &&
- buf->state != UVC_BUF_STATE_ACTIVE)
+ buf->state != UVC_BUF_STATE_ACTIVE &&
+ buf->state != UVC_BUF_STATE_READY)
? 0 : -EAGAIN;
}
return wait_event_interruptible(buf->wait,
buf->state != UVC_BUF_STATE_QUEUED &&
- buf->state != UVC_BUF_STATE_ACTIVE);
+ buf->state != UVC_BUF_STATE_ACTIVE &&
+ buf->state != UVC_BUF_STATE_READY);
}
/*
@@ -348,6 +351,7 @@
case UVC_BUF_STATE_IDLE:
case UVC_BUF_STATE_QUEUED:
case UVC_BUF_STATE_ACTIVE:
+ case UVC_BUF_STATE_READY:
default:
uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state %u "
"(driver bug?).\n", buf->state);
@@ -489,6 +493,7 @@
spin_lock_irqsave(&queue->irqlock, flags);
list_del(&buf->queue);
+ buf->state = UVC_BUF_STATE_DONE;
if (!list_empty(&queue->irqqueue))
nextbuf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
queue);