From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754076Ab1JRUyv (ORCPT ); Tue, 18 Oct 2011 16:54:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61943 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751912Ab1JRUyu (ORCPT ); Tue, 18 Oct 2011 16:54:50 -0400 Date: Tue, 18 Oct 2011 16:54:41 -0400 From: Jason Baron To: Gleb Natapov Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Steven Rostedt Subject: Re: [PATCH] jump_label_inc may return before the code is patched Message-ID: <20111018205441.GC2453@redhat.com> References: <20111018175551.GH17571@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111018175551.GH17571@redhat.com> User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 18, 2011 at 07:55:51PM +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. > > 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(); > } > agreed, we shouldn't return before the update happens...did this cause any actual problem in practice? Or just observed from code inspection? Acked-by: Jason Baron Thanks, -Jason