From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: [PATCH] jbd2: Fix forever sleeping process in do_get_write_access() Date: Thu, 5 May 2011 14:10:39 +0200 Message-ID: <1304597439-7185-1-git-send-email-jack@suse.cz> Cc: Tao Ma , linux-ext4@vger.kernel.org, Jan Kara To: tytso@mit.edu Return-path: Received: from cantor2.suse.de ([195.135.220.15]:58734 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751159Ab1EEMKr (ORCPT ); Thu, 5 May 2011 08:10:47 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 --- fs/jbd2/commit.c | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-) Analogous JBD fix has been queued in my tree... 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); -- 1.7.1