[mythtv-users] Kernel Crash when starting up in au0828-video.c line 895

[Larry Finger]

On 04/08/2012 04:38 PM, jrh wrote:

As you have seen, someone did not like my patch. That frequently happens when 
you try to touch a new area of the kernel. Thus, we need to find the real bug 
before any patch is likely to be accepted.

To help debug the problem, I have prepared a new version of the patch. This one 
will still remove the BUG_ON, but it will also dump the stack whenever the code 
gets or frees AU0828_RESOURCE_VIDEO. I hope this shows where the imbalance occurs.

Larry
-------------- next part --------------
Index: linux-3.1.9-1.4/drivers/media/video/au0828/au0828-video.c
===================================================================
--- linux-3.1.9-1.4.orig/drivers/media/video/au0828/au0828-video.c
+++ linux-3.1.9-1.4/drivers/media/video/au0828/au0828-video.c
@@ -891,8 +891,13 @@ static int res_locked(struct au0828_dev
 static void res_free(struct au0828_fh *fh, unsigned int bits)
 {
 	struct au0828_dev    *dev = fh->dev;
+	unsigned int bits2 = fh->resources & bits;
 
-	BUG_ON((fh->resources & bits) != bits);
+	if (bits2 != bits) {
+		WARN_ONCE(true, "au0828: Trying to free resource 0x%x"
+			  " without reserving it\n", bits);
+		return;
+	}
 
 	mutex_lock(&dev->lock);
 	fh->resources  &= ~bits;
@@ -1050,6 +1055,8 @@ static int au0828_v4l2_close(struct file
 
 		videobuf_stop(&fh->vb_vidq);
 		res_free(fh, AU0828_RESOURCE_VIDEO);
+		pr_info("AU0828_RESOURCE_VIDEO freed\n");
+		dump_stack();
 	}
 
 	if (res_check(fh, AU0828_RESOURCE_VBI)) {
@@ -1138,8 +1145,13 @@ static unsigned int au0828_v4l2_poll(str
 		return rc;
 
 	if (fh->type == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
-		if (!res_get(fh, AU0828_RESOURCE_VIDEO))
+		if (!res_get(fh, AU0828_RESOURCE_VIDEO)) {
+			pr_err("AU0828_RESOURCE_VIDEO was busy\n");
+			dump_stack();
 			return POLLERR;
+		}
+		pr_info("AU0828_RESOURCE_VIDEO acquired\n");
+		dump_stack();
 		return videobuf_poll_stream(filp, &fh->vb_vidq, wait);
 	} else if (fh->type == V4L2_BUF_TYPE_VBI_CAPTURE) {
 		if (!res_get(fh, AU0828_RESOURCE_VBI))
@@ -1694,6 +1706,8 @@ static int vidioc_streamoff(struct file
 
 		videobuf_streamoff(&fh->vb_vidq);
 		res_free(fh, AU0828_RESOURCE_VIDEO);
+		pr_info("AU0828_RESOURCE_VIDEO freed\n");
+		dump_stack();
 	} else if (fh->type == V4L2_BUF_TYPE_VBI_CAPTURE) {
 		dev->vbi_timeout_running = 0;
 		del_timer_sync(&dev->vbi_timeout);