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 3.15-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-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 Mon Sep 17 00:00:00 2001
From: Al Viro <[email protected]>
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 <[email protected]>
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 <[email protected]>
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/dcache.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -532,10 +532,12 @@ 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 [email protected]
are
queue-3.15/lock_parent-don-t-step-on-stale-d_parent-of-all-but-freed-one.patch
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