From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965661AbbHKRH6 (ORCPT ); Tue, 11 Aug 2015 13:07:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39924 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965545AbbHKRGT (ORCPT ); Tue, 11 Aug 2015 13:06:19 -0400 Date: Tue, 11 Aug 2015 19:04:04 +0200 From: Oleg Nesterov To: Al Viro , Dave Chinner , Dave Hansen , Jan Kara Cc: "Paul E. McKenney" , Peter Zijlstra , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/8] document rwsem_release() in sb_wait_write() Message-ID: <20150811170404.GA26911@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150811170343.GA26881@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Not only we need to avoid the warning from lockdep_sys_exit(), the caller of freeze_super() can never release this lock. Another thread can do this, so there is another reason for rwsem_release(). Plus the comment should explain why we have to fool lockdep. Signed-off-by: Oleg Nesterov --- fs/super.c | 12 +++++++++--- 1 files changed, 9 insertions(+), 3 deletions(-) diff --git a/fs/super.c b/fs/super.c index d0fdd49..89b58fb 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1236,11 +1236,17 @@ static void sb_wait_write(struct super_block *sb, int level) { s64 writers; + rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_); /* - * We just cycle-through lockdep here so that it does not complain - * about returning with lock to userspace + * We are going to return to userspace and forget about this lock, the + * ownership goes to the caller of thaw_super() which does unlock. + * + * FIXME: we should do this before return from freeze_super() after we + * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super() + * should re-acquire these locks before s_op->unfreeze_fs(sb). However + * this leads to lockdep false-positives, so currently we do the early + * release right after acquire. */ - rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_); rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_); do { -- 1.5.5.1