loop: clear wb_err in bd_inode when detaching backing file

From: Jeff Layton <[email protected]>

When a loop block device encounters a writeback error, that error will get propagated to the bd_inode's wb_err field. If we then detach the backing file from it, attach another and fsync it, we'll get back the writeback error that we had from the previous backing file.

This is a bit of a grey area as POSIX doesn't cover loop devices, but it is somewhat counterintuitive.

If we detach a backing file from the loopdev while there are still unreported errors, take it as a sign that we're no longer interested in the previous file, and clear out the wb_err in the loop blockdev.

---
 drivers/block/loop.c | 1 +
 1 file changed, 1 insertion(+)

Resend to fix the attributions.

index 5d4e31655d96..55cf554bc914 100644
@@ -1068,6 +1068,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	if (bdev) {
 		bdput(bdev);
 		invalidate_bdev(bdev);
+		bdev->bd_inode->i_mapping->wb_err = 0;
 	}
 	set_capacity(lo->lo_disk, 0);
 	loop_sysfs_exit(lo);

2.17.0

Applied, thanks Jeff.

Jens Axboe