From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941644AbcJYLd5 convert rfc822-to-8bit (ORCPT ); Tue, 25 Oct 2016 07:33:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48212 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932654AbcJYLd4 (ORCPT ); Tue, 25 Oct 2016 07:33:56 -0400 Date: Tue, 25 Oct 2016 13:33:47 +0200 From: Jesper Dangaard Brouer To: Arnd Bergmann Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vladimir Davydov , Johannes Weiner , Laura Abbott , Alexander Potapenko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, brouer@redhat.com, Alexander Duyck Subject: Re: [PATCH] slub: avoid false-postive warning Message-ID: <20161025133347.73b501fc@redhat.com> In-Reply-To: <20161024155704.3114445-1-arnd@arndb.de> References: <20161024155704.3114445-1-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 25 Oct 2016 11:33:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 24 Oct 2016 17:56:13 +0200 Arnd Bergmann wrote: > The slub allocator gives us some incorrect warnings when > CONFIG_PROFILE_ANNOTATED_BRANCHES is set, as the unlikely() > macro prevents it from seeing that the return code matches > what it was before: > > mm/slub.c: In function ‘kmem_cache_free_bulk’: > mm/slub.c:262:23: error: ‘df.s’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > mm/slub.c:2943:3: error: ‘df.cnt’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > mm/slub.c:2933:4470: error: ‘df.freelist’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > mm/slub.c:2943:3: error: ‘df.tail’ may be used uninitialized in this function [-Werror=maybe-uninitialized] > > I have not been able to come up with a perfect way for dealing with > this, the three options I see are: > > - add a bogus initialization, which would increase the runtime overhead > - replace unlikely() with unlikely_notrace() > - remove the unlikely() annotation completely > > I checked the object code for a typical x86 configuration and the > last two cases produce the same result, so I went for the last > one, which is the simplest. If the object code is the same, then I've fine with this solution, as the performance should then also be the same. I do have micro-benchmark module there to verify the performance: https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/slab_bulk_test01.c Acked-by: Jesper Dangaard Brouer > Signed-off-by: Arnd Bergmann > --- > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 2b3e740609e9..68b84f93d38d 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3076,7 +3076,7 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p) > struct detached_freelist df; > > size = build_detached_freelist(s, size, p, &df); > - if (unlikely(!df.page)) > + if (!df.page) > continue; > > slab_free(df.s, df.page, df.freelist, df.tail, df.cnt,_RET_IP_); -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer