From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] jbd2: Fix forever sleeping process in do_get_write_access() Date: Thu, 5 May 2011 16:11:14 +0200 Message-ID: <20110505141114.GG5323@quack.suse.cz> References: <1304597439-7185-1-git-send-email-jack@suse.cz> <4DC2AADA.9070708@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , tytso@mit.edu, Tao Ma , linux-ext4@vger.kernel.org To: Eric Sandeen Return-path: Received: from cantor2.suse.de ([195.135.220.15]:35367 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755199Ab1EEOL0 (ORCPT ); Thu, 5 May 2011 10:11:26 -0400 Content-Disposition: inline In-Reply-To: <4DC2AADA.9070708@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu 05-05-11 08:49:14, Eric Sandeen wrote: > On 5/5/11 7:10 AM, Jan Kara wrote: > > 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. > > needed for jbd/commit.c as well, I guess? Yes, I was already queued in my tree. I just sent it to the list as well. Honza > > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c > > index 2e5d370..3a958c7 100644 > > --- a/fs/jbd2/commit.c > > +++ b/fs/jbd2/commit.c > > @@ -768,8 +768,13 @@ wait_for_iobuf: > > required. */ > > JBUFFER_TRACE(jh, "file as BJ_Forget"); > > jbd2_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 > > + * jbd2_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); > -- Jan Kara SUSE Labs, CR