autofs: revert "autofs: take more care to not update last_used on path walk"

While commit 092a5345 ("autofs: take more care to not update
last_used on path walk") helped (partially) resolve a problem where
automounts were not expiring due to aggressive accesses from user space
it has a side effect for very large environments.

This change helps with the expire problem by making the expire more
aggressive but, for very large environments, that means more mount
requests from clients.  When there are a lot of clients that can mean
fairly significant server load increases.

It turns out I put the last_used in this position to solve this very
problem and failed to update my own thinking of the autofs expire
policy.  So the patch being reverted introduces a regression which
should be fixed.

Link: http://lkml.kernel.org/r/151174729420.6162.1832622523537052460.stgit@pluto.themaw.net
Fixes: 092a5345 ("autofs: take more care to not update last_used on path walk")
Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: NeilBrown <neilb@suse.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org>	[4.11+]
Cc: Colin Walters <walters@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Ondrej Holy <oholy@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/root.c

@@ -281,8 +281,8 @@ static int autofs4_mount_wait(const struct path *path, bool rcu_walk)
 		pr_debug("waiting for mount name=%pd\n", path->dentry);
 		status = autofs4_wait(sbi, path, NFY_MOUNT);
 		pr_debug("mount wait done status=%d\n", status);
-		ino->last_used = jiffies;
 	}
+	ino->last_used = jiffies;
 	return status;
 }
 
@@ -321,21 +321,16 @@ static struct dentry *autofs4_mountpoint_changed(struct path *path)
 	 */
 	if (autofs_type_indirect(sbi->type) && d_unhashed(dentry)) {
 		struct dentry *parent = dentry->d_parent;
+		struct autofs_info *ino;
 		struct dentry *new;
 
 		new = d_lookup(parent, &dentry->d_name);
 		if (!new)
 			return NULL;
-		if (new == dentry)
-			dput(new);
-		else {
-			struct autofs_info *ino;
-
-			ino = autofs4_dentry_ino(new);
-			ino->last_used = jiffies;
-			dput(path->dentry);
-			path->dentry = new;
-		}
+		ino = autofs4_dentry_ino(new);
+		ino->last_used = jiffies;
+		dput(path->dentry);
+		path->dentry = new;
 	}
 	return path->dentry;
 }