rbd: don't revalidate so much

Whenever a header object event causes a mapped rbd image to refresh
its header information, revalidate_disk() is being called.  This was
done in rbd_dev_refresh() outside the control mutex in order to
avoid a lock inversion.  Although a an event like this *might*
indicate the image has changed size, most of the time it does not.

Record the image size before and after the refresh, and only
call revalidate_disk() if it changes.

This resolves:
    http://tracker.ceph.com/issues/4867

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 71e2de2cff22..ab2c788a22ad 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3065,19 +3065,22 @@ static int rbd_dev_v1_refresh(struct rbd_device *rbd_dev, u64 *hver)
 
 static int rbd_dev_refresh(struct rbd_device *rbd_dev, u64 *hver)
 {
+        u64 image_size;
         int ret;
 
         rbd_assert(rbd_image_format_valid(rbd_dev->image_format));
+        image_size = rbd_dev->header.image_size;
         mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
         if (rbd_dev->image_format == 1)
                 ret = rbd_dev_v1_refresh(rbd_dev, hver);
         else
                 ret = rbd_dev_v2_refresh(rbd_dev, hver);
         mutex_unlock(&ctl_mutex);
-        revalidate_disk(rbd_dev->disk);
         if (ret)
                 rbd_warn(rbd_dev, "got notification but failed to "
                            " update snaps: %d\n", ret);
+        if (image_size != rbd_dev->header.image_size)
+                revalidate_disk(rbd_dev->disk);
 
         return ret;
 }