From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756782Ab1FPHXk (ORCPT ); Thu, 16 Jun 2011 03:23:40 -0400 Received: from out4.smtp.messagingengine.com ([66.111.4.28]:38863 "EHLO out4.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756737Ab1FPHKQ (ORCPT ); Thu, 16 Jun 2011 03:10:16 -0400 X-Sasl-enc: P1wH8NXgimS3zZh9ycCbr4SxdyhwemzbOmyVG4bsLz1c 1308208215 X-Mailbox-Line: From gregkh@clark.kroah.org Wed Jun 15 17:29:04 2011 Message-Id: <20110616002904.893535644@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Wed, 15 Jun 2011 17:28:07 -0700 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 Subject: [11/85] jbd: Fix forever sleeping process in do_get_write_access() In-Reply-To: <20110616002917.GA3627@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.33-longterm review patch. If anyone has any objections, please let us know. ------------------ 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 @@ -746,8 +746,13 @@ 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);