linux-kernel - [PATCH 6/7] autofs - dont hold spin lock over direct mount expire

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Date:   Mon, 28 Nov 2016 10:12:14 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Omar Sandoval <osandov@...ndov.com>,
        Al Viro <viro@...IV.linux.org.uk>
Subject: [PATCH 6/7] autofs - dont hold spin lock over direct mount expire

From: Ian Kent <ikent@...hat.com>

Commit 7cbdb4a286 altered the autofs indirect mount expire to
not hold a spin lock during the expire check.

The direct mount expire needs the same treatment because to
make autofs expires namespace aware may_umount_tree() needs to
to use a similar method to may_umount() when checking if a mount
tree is in use.

This means may_umount_tree() will end up taking the namespace_sem
for the check so the autofs direct mount expire won't be allowed
to hold a spin lock over the check.

Signed-off-by: Ian Kent <raven@...maw.net>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Omar Sandoval <osandov@...ndov.com>
---
 fs/autofs4/expire.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 13178bf..57725d4 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -310,26 +310,29 @@ struct dentry *autofs4_expire_direct(struct super_block *sb,
 	now = jiffies;
 	timeout = sbi->exp_timeout;
 
-	spin_lock(&sbi->fs_lock);
-	ino = autofs4_dentry_ino(root);
-	/* No point expiring a pending mount */
-	if (ino->flags & AUTOFS_INF_PENDING)
-		goto out;
 	if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
+		spin_lock(&sbi->fs_lock);
+		ino = autofs4_dentry_ino(root);
+		/* No point expiring a pending mount */
+		if (ino->flags & AUTOFS_INF_PENDING) {
+			spin_unlock(&sbi->fs_lock);
+			goto out;
+		}
 		ino->flags |= AUTOFS_INF_WANT_EXPIRE;
 		spin_unlock(&sbi->fs_lock);
 		synchronize_rcu();
-		spin_lock(&sbi->fs_lock);
 		if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
+			spin_lock(&sbi->fs_lock);
 			ino->flags |= AUTOFS_INF_EXPIRING;
 			init_completion(&ino->expire_complete);
 			spin_unlock(&sbi->fs_lock);
 			return root;
 		}
+		spin_lock(&sbi->fs_lock);
 		ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;
+		spin_unlock(&sbi->fs_lock);
 	}
 out:
-	spin_unlock(&sbi->fs_lock);
 	dput(root);
 
 	return NULL;