Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752393Ab0AWVgi (ORCPT ); Sat, 23 Jan 2010 16:36:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752029Ab0AWVgh (ORCPT ); Sat, 23 Jan 2010 16:36:37 -0500 Received: from fanny.its.uu.se ([130.238.4.241]:2256 "EHLO fanny.its.uu.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752002Ab0AWVgg (ORCPT ); Sat, 23 Jan 2010 16:36:36 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <19291.27613.146510.938088@pilspetsen.it.uu.se> Date: Sat, 23 Jan 2010 22:36:29 +0100 From: Mikael Pettersson To: linux-kernel@vger.kernel.org Subject: [PATCH 2.6.33-rc5] futex_lock_pi() key refcnt fix Cc: Peter Zijlstra X-Mailer: VM 7.17 under Emacs 20.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2259 Lines: 49 This fixes a futex key reference count bug in futex_lock_pi(), where a key's reference count is incremented twice but decremented only once, causing the backing object to not be released. If the futex is created in a temporary file in an ext3 file system, this bug causes the file's inode to become an "undead" orphan, which causes an oops from a BUG_ON() in ext3_put_super() when the file system is unmounted. glibc's test suite is known to trigger this, see . The bug is a regression from 2.6.28-git3, namely Peter Zijlstra's 38d47c1b7075bd7ec3881141bb3629da58f88dab "[PATCH] futex: rely on get_user_pages() for shared futexes". That commit made get_futex_key() also increment the reference count of the futex key, and updated its callers to decrement the key's reference count before returning. Unfortunately the normal exit path in futex_lock_pi() wasn't corrected: the reference count is incremented by get_futex_key() and queue_lock(), but the normal exit path only decrements once, via unqueue_me_pi(). The fix is to put_futex_key() after unqueue_me_pi(), since 2.6.31 this is easily done by 'goto out_put_key' rather than 'goto out'. Signed-off-by: Mikael Pettersson Cc: --- This patch also works for backports to 2.6.32 and 2.6.31, but 2.6.30 and 2.6.29 need a "put_futex_key(fshared, &q.key);" after "unqueue_me_pi(&q);" instead. I can supply patches for these older kernels if necessary. kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -rupN linux-2.6.33-rc5/kernel/futex.c linux-2.6.33-rc5.futex_lock_pi-key-refcnt-fix/kernel/futex.c --- linux-2.6.33-rc5/kernel/futex.c 2010-01-22 01:21:57.000000000 +0100 +++ linux-2.6.33-rc5.futex_lock_pi-key-refcnt-fix/kernel/futex.c 2010-01-23 21:00:14.000000000 +0100 @@ -1971,7 +1971,7 @@ retry_private: /* Unqueue and drop the lock */ unqueue_me_pi(&q); - goto out; + goto out_put_key; out_unlock_put_key: queue_unlock(&q, hb); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/