[PATCH V2] poll method lose race condition

["Figo.zhang" <figo1802@gmail.com>]

 bttv-driver.c,cx23885-video.c,cx88-video.c: poll method lose race condition for capture video.

 In v2, use the clear logic.Thanks to Trent Piepho's help.

Signed-off-by: Figo.zhang <figo1802@gmail.com>
---
 drivers/media/video/bt8xx/bttv-driver.c     |   20 ++++++++++++--------
 drivers/media/video/cx23885/cx23885-video.c |   15 +++++++++++----
 drivers/media/video/cx88/cx88-video.c       |   15 +++++++++++----
 3 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/drivers/media/video/bt8xx/bttv-driver.c b/drivers/media/video/bt8xx/bttv-driver.c
index 23b7499..8d20528 100644
--- a/drivers/media/video/bt8xx/bttv-driver.c
+++ b/drivers/media/video/bt8xx/bttv-driver.c
@@ -3152,6 +3152,7 @@ static unsigned int bttv_poll(struct file *file, poll_table *wait)
 	struct bttv_fh *fh = file->private_data;
 	struct bttv_buffer *buf;
 	enum v4l2_field field;
+	unsigned int rc = POLLERR;
 
 	if (V4L2_BUF_TYPE_VBI_CAPTURE == fh->type) {
 		if (!check_alloc_btres(fh->btv,fh,RESOURCE_VBI))
@@ -3160,9 +3161,10 @@ static unsigned int bttv_poll(struct file *file, poll_table *wait)
 	}
 
 	if (check_btres(fh,RESOURCE_VIDEO_STREAM)) {
+		mutex_lock(&fh->cap.vb_lock);
 		/* streaming capture */
 		if (list_empty(&fh->cap.stream))
-			return POLLERR;
+			return done;
 		buf = list_entry(fh->cap.stream.next,struct bttv_buffer,vb.stream);
 	} else {
 		/* read() capture */
@@ -3170,16 +3172,16 @@ static unsigned int bttv_poll(struct file *file, poll_table *wait)
 		if (NULL == fh->cap.read_buf) {
 			/* need to capture a new frame */
 			if (locked_btres(fh->btv,RESOURCE_VIDEO_STREAM))
-				goto err;
+				goto done;
 			fh->cap.read_buf = videobuf_sg_alloc(fh->cap.msize);
 			if (NULL == fh->cap.read_buf)
-				goto err;
+				goto done;
 			fh->cap.read_buf->memory = V4L2_MEMORY_USERPTR;
 			field = videobuf_next_field(&fh->cap);
 			if (0 != fh->cap.ops->buf_prepare(&fh->cap,fh->cap.read_buf,field)) {
 				kfree (fh->cap.read_buf);
 				fh->cap.read_buf = NULL;
-				goto err;
+				goto done;
 			}
 			fh->cap.ops->buf_queue(&fh->cap,fh->cap.read_buf);
 			fh->cap.read_off = 0;
@@ -3191,11 +3193,13 @@ static unsigned int bttv_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &buf->vb.done, wait);
 	if (buf->vb.state == VIDEOBUF_DONE ||
 	    buf->vb.state == VIDEOBUF_ERROR)
-		return POLLIN|POLLRDNORM;
-	return 0;
-err:
+		rc =  POLLIN|POLLRDNORM;
+	else 
+		rc = 0;
+	
+done:
 	mutex_unlock(&fh->cap.vb_lock);
-	return POLLERR;
+	return rc;
 }
 
 static int bttv_open(struct file *file)
diff --git a/drivers/media/video/cx23885/cx23885-video.c b/drivers/media/video/cx23885/cx23885-video.c
index 68068c6..f542493 100644
--- a/drivers/media/video/cx23885/cx23885-video.c
+++ b/drivers/media/video/cx23885/cx23885-video.c
@@ -796,6 +796,7 @@ static unsigned int video_poll(struct file *file,
 {
 	struct cx23885_fh *fh = file->private_data;
 	struct cx23885_buffer *buf;
+	unsigned int rc = POLLERR;
 
 	if (V4L2_BUF_TYPE_VBI_CAPTURE == fh->type) {
 		if (!res_get(fh->dev, fh, RESOURCE_VBI))
@@ -803,23 +804,29 @@ static unsigned int video_poll(struct file *file,
 		return videobuf_poll_stream(file, &fh->vbiq, wait);
 	}
 
+	mutex_lock(&fh->vidq.vb_lock);
 	if (res_check(fh, RESOURCE_VIDEO)) {
 		/* streaming capture */
 		if (list_empty(&fh->vidq.stream))
-			return POLLERR;
+			goto done;
 		buf = list_entry(fh->vidq.stream.next,
 			struct cx23885_buffer, vb.stream);
 	} else {
 		/* read() capture */
 		buf = (struct cx23885_buffer *)fh->vidq.read_buf;
 		if (NULL == buf)
-			return POLLERR;
+			goto done;
 	}
 	poll_wait(file, &buf->vb.done, wait);
 	if (buf->vb.state == VIDEOBUF_DONE ||
 	    buf->vb.state == VIDEOBUF_ERROR)
-		return POLLIN|POLLRDNORM;
-	return 0;
+		rc =  POLLIN|POLLRDNORM;
+	else
+		rc = 0;
+
+done:
+	mutex_unlock(&fh->vidq.vb_lock);
+	return rc;
 }
 
 static int video_release(struct file *file)
diff --git a/drivers/media/video/cx88/cx88-video.c b/drivers/media/video/cx88/cx88-video.c
index b993d42..b1ca54b 100644
--- a/drivers/media/video/cx88/cx88-video.c
+++ b/drivers/media/video/cx88/cx88-video.c
@@ -869,6 +869,7 @@ video_poll(struct file *file, struct poll_table_struct *wait)
 {
 	struct cx8800_fh *fh = file->private_data;
 	struct cx88_buffer *buf;
+	unsigned int rc = POLLERR;
 
 	if (V4L2_BUF_TYPE_VBI_CAPTURE == fh->type) {
 		if (!res_get(fh->dev,fh,RESOURCE_VBI))
@@ -876,22 +877,28 @@ video_poll(struct file *file, struct poll_table_struct *wait)
 		return videobuf_poll_stream(file, &fh->vbiq, wait);
 	}
 
+	mutex_lock(&fh->vidq.vb_lock);
 	if (res_check(fh,RESOURCE_VIDEO)) {
 		/* streaming capture */
 		if (list_empty(&fh->vidq.stream))
-			return POLLERR;
+			goto done;
 		buf = list_entry(fh->vidq.stream.next,struct cx88_buffer,vb.stream);
 	} else {
 		/* read() capture */
 		buf = (struct cx88_buffer*)fh->vidq.read_buf;
 		if (NULL == buf)
-			return POLLERR;
+			goto done;
 	}
 	poll_wait(file, &buf->vb.done, wait);
 	if (buf->vb.state == VIDEOBUF_DONE ||
 	    buf->vb.state == VIDEOBUF_ERROR)
-		return POLLIN|POLLRDNORM;
-	return 0;
+		rc =  POLLIN|POLLRDNORM;
+	else
+		rc = 0;
+
+done:
+	mutex_unlock(&fh->vidq.vb_lock);
+	return rc;
 }
 
 static int video_release(struct file *file)