Avoid ELOOP on auto-mounted snapshots

Ensure that the path member pointers are associated with the
newly-mounted snapshot when zpl_snapdir_automount() returns.  Otherwise
the follow_automount() function may be called repeatedly, leading to an
incorrect ELOOP error return. This problem was observed as a 'Too many
levels of symbolic links' error from user-space commands accessing an
unmounted snapshot in the .zfs/snapshot directory.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #816

diff --git a/module/zfs/zpl_ctldir.c b/module/zfs/zpl_ctldir.c
index 7dfaf6e..a2d8fa9 100644 (file)
--- a/module/zfs/zpl_ctldir.c
+++ b/module/zfs/zpl_ctldir.c
@@ -357,6 +357,13 @@ zpl_snapdir_automount(struct path *path)
                return ERR_PTR(error);
 
        /*
+        * Ensure path->dentry points to the dentry for the root of the
+        * newly-mounted snapshot, otherwise this function may be called
+        * repeatedly which can lead to an incorrect ELOOP error return.
+        */
+       follow_up(path);
+
+       /*
         * Rather than returning the new vfsmount for the snapshot we must
         * return NULL to indicate a mount collision.  This is done because
         * the user space mount calls do_add_mount() which adds the vfsmount