From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f66.google.com ([74.125.82.66]:54353 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751355AbeCHMaR (ORCPT ); Thu, 8 Mar 2018 07:30:17 -0500 Received: by mail-wm0-f66.google.com with SMTP id z81so10929744wmb.4 for ; Thu, 08 Mar 2018 04:30:17 -0800 (PST) Subject: Re: [PATCH 1/2] btrfs: introduce conditional wakeup helpers To: David Sterba , linux-btrfs@vger.kernel.org References: <96b9c7113ac06d981c3f69638762c4502651f6af.1520509627.git.dsterba@suse.com> From: Nikolay Borisov Message-ID: Date: Thu, 8 Mar 2018 14:30:14 +0200 MIME-Version: 1.0 In-Reply-To: <96b9c7113ac06d981c3f69638762c4502651f6af.1520509627.git.dsterba@suse.com> Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 8.03.2018 13:49, David Sterba wrote: > Add convenience wrappers for the waitqueue management that involves > memory barriers to prevent deadlocks. The helpers will let us remove > barriers and the necessary comments in several places. > > Signed-off-by: David Sterba Reviewed-by: Nikolay Borisov > --- > fs/btrfs/ctree.h | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index bf545e7552b8..c9827a1b676d 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -3748,4 +3748,27 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info) > #endif > return 0; > } > + > +static inline void cond_wake_up(struct wait_queue_head *wq) > +{ > + /* > + * This implies a full smp_mb barrier, see comments for > + * waitqueue_active why. > + */ > + if (wq_has_sleeper(wq)) > + wake_up(wq); > +} > + > +static inline void cond_wake_up_nomb(struct wait_queue_head *wq) > +{ > + /* > + * Special case for conditional wakeup where the barrier required for > + * waitqueue_active is implied by some of the preceding code. Eg. one > + * of such atomic operations (atomic_dec_and_return, ...), or a > + * unlock/lock sequence, etc. > + */ > + if (waitqueue_active(wq)) > + wake_up(wq); > +} > + > #endif >