Patch "autofs: revert "autofs: take more care to not update last_used on path walk"" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
autofs-revert-autofs-take-more-care-to-not-update-last_used-on-path-walk.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ian Kent <[email protected]>
Date: Wed, 29 Nov 2017 16:11:23 -0800
Subject: autofs: revert "autofs: take more care to not update last_used on path walk"

From: Ian Kent <[email protected]>

commit 43694d4bf843ddd34519e8e9de983deefeada699 upstream.

While commit 092a53452bb7 ("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.

---
 fs/autofs4/root.c |   17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

@@ -281,8 +281,8 @@ static int autofs4_mount_wait(const stru
 		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
 	 */
 	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;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/autofs-revert-autofs-fix-at_no_automount-not-being-honored.patch queue-4.14/autofs-revert-autofs-take-more-care-to-not-update-last_used-on-path-walk.patch