V4L/DVB: gspca - main: Don't use the frame buffer flags

This patch fixes possible race conditions in queue management with SMP:
when a frame was completed, the irq function tried to use the next frame
buffer. At this time, it was possible that the application on an other
processor updated the frame pointer, making the image to point to a bad
buffer.
The patch contains two main changes:
- the image transfer uses the queue indexes which are protected against
  simultaneous memory access,
- the image pointer which is used for image concatenation is only set at
  interrupt level.
Some subdrivers which used the image pointer have been updated.

Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/media/video/gspca/gspca.h b/drivers/media/video/gspca/gspca.h
index 453e43d66a83..17e55580631e 100644
--- a/drivers/media/video/gspca/gspca.h
+++ b/drivers/media/video/gspca/gspca.h
@@ -178,11 +178,11 @@ struct gspca_dev {
 	u8 *image;				/* image beeing filled */
 	__u32 frsz;				/* frame size */
 	u32 image_len;				/* current length of image */
-	char nframes;				/* number of frames */
-	char fr_i;				/* frame being filled */
-	char fr_q;				/* next frame to queue */
-	char fr_o;				/* next frame to dequeue */
+	atomic_t fr_q;				/* next frame to queue */
+	atomic_t fr_i;				/* frame being filled */
 	signed char fr_queue[GSPCA_MAX_FRAMES];	/* frame queue */
+	char nframes;				/* number of frames */
+	u8 fr_o;				/* next frame to dequeue */
 	__u8 last_packet_type;
 	__s8 empty_packet;		/* if (-1) don't check empty packets */
 	__u8 streaming;