From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail333.us4.mandrillapp.com ([205.201.137.77]:42851 "EHLO mail333.us4.mandrillapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754258AbcCAXvJ (ORCPT ); Tue, 1 Mar 2016 18:51:09 -0500 Received: from pmta03.dal05.mailchimp.com (127.0.0.1) by mail333.us4.mandrillapp.com id hqoleq174nov for ; Tue, 1 Mar 2016 23:51:00 +0000 (envelope-from ) From: Greg Kroah-Hartman Subject: [PATCH 3.14 032/130] lock_parent: dont step on stale ->d_parent of all-but-freed one To: Cc: Greg Kroah-Hartman , , Al Viro Message-Id: <20160301234500.894856844@linuxfoundation.org> In-Reply-To: <20160301234459.768886030@linuxfoundation.org> References: <20160301234459.768886030@linuxfoundation.org> Date: Tue, 01 Mar 2016 23:51:00 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro 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 Signed-off-by: Greg Kroah-Hartman --- 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);