Commit 02bbcb9d authored Jul 06, 2010 by Jean-François Moine Committed by Mauro Carvalho Chehab Aug 02, 2010

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>

parent 9059cd44

drivers/media/video/gspca/gspca.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -466,8 +466,9 @@ void gspca_frame_add(struct gspca_dev *gspca_dev,
		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;

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