linux-kernel - [PATCH 7/7] autofs - take more care to not update last

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Message-ID: <148577167169.9801.1377050092212016834.stgit@pluto.themaw.net>
Date:   Mon, 30 Jan 2017 18:21:11 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Tomohiro Kusumi <kusumi.tomohiro@...il.com>,
        autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 7/7] autofs - take more care to not update last_used on path
 walk

GUI environments seem to be becoming more agressive at scanning
filesystems, to the point where autofs cannot expire mounts at
all.

This is one key reason the update of the autofs dentry info
last_used field is done in the expire system when the dentry
is seen to be in use.

But somewhere along the way instances of the update has crept
back into the autofs path walk functions which, with the more
aggressive file access patterns, is preventing expiration.

Changing the update in the path walk functions allows autofs
to at least make progress in spite of frequent immediate
re-mounts from file accesses.

Signed-off-by: Ian Kent <raven@...maw.net>
---
 fs/autofs4/root.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index a11f731..6ddd4fa 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -281,8 +281,8 @@ static int autofs4_mount_wait(struct dentry *dentry, bool rcu_walk)
 		pr_debug("waiting for mount name=%pd\n", dentry);
 		status = autofs4_wait(sbi, dentry, NFY_MOUNT);
 		pr_debug("mount wait done status=%d\n", status);
+		ino->last_used = jiffies;
 	}
-	ino->last_used = jiffies;
 	return status;
 }
 
@@ -319,16 +319,21 @@ 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;
-		ino = autofs4_dentry_ino(new);
-		ino->last_used = jiffies;
-		dput(path->dentry);
-		path->dentry = new;
+		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;
+		}
 	}
 	return path->dentry;
 }