V4L/DVB: gspca - main: Possible race condition in queue management
The problem may occur with SMP:
- a frame is completed at interrupt level (in gspca_frame_add with
packet_type == LAST_PACKET,
- just after clearing the bit V4L2_BUF_FLAG_QUEUED and before setting
the bit V4L2_BUF_FLAG_DONE, on the other processor, the application
tries to requeue the same frame buffer,
- then, the qbuf function succeeds because ALL_FLAGS are not set.
The fix sets and resets the two flags in one instruction.
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>
diff --git a/drivers/media/video/gspca/gspca.c b/drivers/media/video/gspca/gspca.c
index 8e822ed..2dc7270 100644
--- a/drivers/media/video/gspca/gspca.c
+++ b/drivers/media/video/gspca/gspca.c
@@ -466,8 +466,9 @@
j = gspca_dev->fr_queue[i];
frame = &gspca_dev->frame[j];
frame->v4l2_buf.bytesused = gspca_dev->image_len;
- frame->v4l2_buf.flags &= ~V4L2_BUF_FLAG_QUEUED;
- frame->v4l2_buf.flags |= V4L2_BUF_FLAG_DONE;
+ frame->v4l2_buf.flags = (frame->v4l2_buf.flags
+ | V4L2_BUF_FLAG_DONE)
+ & ~V4L2_BUF_FLAG_QUEUED;
wake_up_interruptible(&gspca_dev->wq); /* event = new frame */
i = (i + 1) % gspca_dev->nframes;
gspca_dev->fr_i = i;