Patch "lock_parent: don't step on stale ->d_parent of all-but-freed one" has been added to the 3.14-stable tree

Patch "lock_parent: don't step on stale ->d_parent of all-but-freed one" has been added to the 3.14-stable tree

[gregkh]

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

    lock_parent: don't step on stale ->d_parent of all-but-freed one

to the 3.14-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:
     lock_parent-don-t-step-on-stale-d_parent-of-all-but-freed-one.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Thu, 12 Jun 2014 00:29:13 -0400
Subject: lock_parent: don't step on stale ->d_parent of all-but-freed one

From: Al Viro <viro@zeniv.linux.org.uk>

commit c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 upstream.

Dentry that had been through (or into) __dentry_kill() might be seen
by shrink_dentry_list(); that's normal, it'll be taken off the shrink
list and freed if __dentry_kill() has already finished.  The problem
is, its ->d_parent might be pointing to already freed dentry, so
lock_parent() needs to be careful.

We need to check that dentry hasn't already gone into __dentry_kill()
*and* grab rcu_read_lock() before dropping ->d_lock - the latter makes
sure that whatever we see in ->d_parent after dropping ->d_lock it
won't be freed until we drop rcu_read_lock().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/dcache.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -530,10 +530,12 @@ static inline struct dentry *lock_parent
 	struct dentry *parent = dentry->d_parent;
 	if (IS_ROOT(dentry))
 		return NULL;
+	if (unlikely((int)dentry->d_lockref.count < 0))
+		return NULL;
 	if (likely(spin_trylock(&parent->d_lock)))
 		return parent;
-	spin_unlock(&dentry->d_lock);
 	rcu_read_lock();
+	spin_unlock(&dentry->d_lock);
 again:
 	parent = ACCESS_ONCE(dentry->d_parent);
 	spin_lock(&parent->d_lock);


Patches currently in stable-queue which might be from viro@zeniv.linux.org.uk are

queue-3.14/lock_parent-don-t-step-on-stale-d_parent-of-all-but-freed-one.patch
queue-3.14/lift-the-already-marked-killed-case-into-shrink_dentry_list.patch
queue-3.14/expand-dentry_kill-dentry-0-in-shrink_dentry_list.patch
queue-3.14/bcache-fix-a-leak-in-bch_cached_dev_run.patch
queue-3.14/dcache-add-missing-lockdep-annotation.patch
queue-3.14/dealing-with-the-rest-of-shrink_dentry_list-livelock.patch
queue-3.14/split-dentry_kill.patch
queue-3.14/shrink_dentry_list-take-parent-s-d_lock-earlier.patch
queue-3.14/dentry_kill-doesn-t-need-the-second-argument-now.patch