Fix a deadlock in the bttv driver

vidiocgmbuf() does this:
        mutex_lock(&fh->cap.vb_lock);
        retval = videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,
                                     V4L2_MEMORY_MMAP);

and videobuf_mmap_setup() then just does
        mutex_lock(&q->vb_lock);
        ret = __videobuf_mmap_setup(q, bcount, bsize, memory);
        mutex_unlock(&q->vb_lock);

which is an obvious double-take deadlock.

This patch fixes this by having vidiocgmbuf() just call the
__videobuf_mmap_setup function instead.

Acked-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Reported-by: Koos Vriezen <koos.vriezen@gmail.com>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/media/video/bt8xx/bttv-driver.c

@@ -2613,7 +2613,7 @@ static int vidiocgmbuf(struct file *file, void *priv, struct video_mbuf *mbuf)
 	struct bttv_fh *fh = priv;
 
 	mutex_lock(&fh->cap.vb_lock);
-	retval = videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,
+	retval = __videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,
 				     V4L2_MEMORY_MMAP);
 	if (retval < 0) {
 		mutex_unlock(&fh->cap.vb_lock);

drivers/media/video/videobuf-core.c

@@ -331,7 +331,7 @@ int videobuf_mmap_free(struct videobuf_queue *q)
 }
 
 /* Locking: Caller holds q->vb_lock */
-static int __videobuf_mmap_setup(struct videobuf_queue *q,
+int __videobuf_mmap_setup(struct videobuf_queue *q,
 			unsigned int bcount, unsigned int bsize,
 			enum v4l2_memory memory)
 {
@@ -1129,6 +1129,7 @@ EXPORT_SYMBOL_GPL(videobuf_read_stream);
 EXPORT_SYMBOL_GPL(videobuf_read_one);
 EXPORT_SYMBOL_GPL(videobuf_poll_stream);
 
+EXPORT_SYMBOL_GPL(__videobuf_mmap_setup);
 EXPORT_SYMBOL_GPL(videobuf_mmap_setup);
 EXPORT_SYMBOL_GPL(videobuf_mmap_free);
 EXPORT_SYMBOL_GPL(videobuf_mmap_mapper);

include/media/videobuf-core.h

@@ -237,6 +237,9 @@ unsigned int videobuf_poll_stream(struct file *file,
 int videobuf_mmap_setup(struct videobuf_queue *q,
 			unsigned int bcount, unsigned int bsize,
 			enum v4l2_memory memory);
+int __videobuf_mmap_setup(struct videobuf_queue *q,
+			unsigned int bcount, unsigned int bsize,
+			enum v4l2_memory memory);
 int videobuf_mmap_free(struct videobuf_queue *q);
 int videobuf_mmap_mapper(struct videobuf_queue *q,
 			 struct vm_area_struct *vma);