From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932998Ab1KBPVq (ORCPT ); Wed, 2 Nov 2011 11:21:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54858 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932944Ab1KBPVn (ORCPT ); Wed, 2 Nov 2011 11:21:43 -0400 Date: Wed, 2 Nov 2011 17:21:23 +0200 From: Gleb Natapov To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Jason Baron , Peter Zijlstra , mingo@elte.hu Subject: Re: [PATCH] jump_label_inc may return before the code is patched Message-ID: <20111102152123.GF14726@redhat.com> References: <20111018175551.GH17571@redhat.com> <1318971986.3712.18.camel@frodo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1318971986.3712.18.camel@frodo> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 18, 2011 at 05:06:25PM -0400, Steven Rostedt wrote: > On Tue, 2011-10-18 at 19:55 +0200, Gleb Natapov wrote: > > If cpu A calls jump_label_inc() just after atomic_add_return() is > > called by cpu B, atomic_inc_not_zero() will return value greater then > > zero and jump_label_inc() will return to a caller before jump_label_update() > > finishes its job on cpu B. > > OK, I see what you are saying. There's a race here that jump_label_inc > may return before jump labels are actually activated. I have no issue > with this change. This guarantees that jump labels will be active on > return of jump_label_inc(). > > I'm assuming that jump_label_update() does memory barries, as it does > modify code, and would be itself a synchronization point. > > Acked-by: Steven Rostedt > So through what tree this should go to Linus' git? > -- Steve > > > > > Signed-off-by: Gleb Natapov > > diff --git a/kernel/jump_label.c b/kernel/jump_label.c > > index a8ce450..e6f1f24 100644 > > --- a/kernel/jump_label.c > > +++ b/kernel/jump_label.c > > @@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key) > > return; > > > > jump_label_lock(); > > - if (atomic_add_return(1, &key->enabled) == 1) > > + if (atomic_read(&key->enabled) == 0) > > jump_label_update(key, JUMP_LABEL_ENABLE); > > + atomic_inc(&key->enabled); > > jump_label_unlock(); > > } > > > > -- > > Gleb. > -- Gleb.