From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162379Ab1FAIT3 (ORCPT ); Wed, 1 Jun 2011 04:19:29 -0400 Received: from cantor.suse.de ([195.135.220.2]:44452 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162361Ab1FAITX (ORCPT ); Wed, 1 Jun 2011 04:19:23 -0400 X-Mailbox-Line: From linux@blue.kroah.org Wed Jun 1 17:11:18 2011 Message-Id: <20110601081117.659328028@blue.kroah.org> User-Agent: quilt/0.48-16.4 Date: Wed, 01 Jun 2011 17:10:18 +0900 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Jan Kara , Greg Kroah-Hartman Subject: [048/165] jbd: Fix forever sleeping process in do_get_write_access() In-Reply-To: <20110601081349.GA10017@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.39-stable review patch. If anyone has any objections, please let us know. ------------------ Content-Length: 1412 Lines: 39 From: Jan Kara commit 2842bb20eed2e25cde5114298edc62c8883a1d9a upstream. In do_get_write_access() we wait on BH_Unshadow bit for buffer to get from shadow state. The waking code in journal_commit_transaction() has a bug because it does not issue a memory barrier after the buffer is moved from the shadow state and before wake_up_bit() is called. Thus a waitqueue check can happen before the buffer is actually moved from the shadow state and waiting process may never be woken. Fix the problem by issuing proper barrier. Reported-by: Tao Ma Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman --- fs/jbd/commit.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/fs/jbd/commit.c +++ b/fs/jbd/commit.c @@ -722,8 +722,13 @@ wait_for_iobuf: required. */ JBUFFER_TRACE(jh, "file as BJ_Forget"); journal_file_buffer(jh, commit_transaction, BJ_Forget); - /* Wake up any transactions which were waiting for this - IO to complete */ + /* + * Wake up any transactions which were waiting for this + * IO to complete. The barrier must be here so that changes + * by journal_file_buffer() take effect before wake_up_bit() + * does the waitqueue check. + */ + smp_mb(); wake_up_bit(&bh->b_state, BH_Unshadow); JBUFFER_TRACE(jh, "brelse shadowed buffer"); __brelse(bh);