From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 2D8FD6B00A3 for ; Thu, 1 Oct 2009 16:49:12 -0400 (EDT) Received: from wpaz21.hot.corp.google.com (wpaz21.hot.corp.google.com [172.24.198.85]) by smtp-out.google.com with ESMTP id n91Kn6tp014314 for ; Thu, 1 Oct 2009 21:49:06 +0100 Received: from pzk15 (pzk15.prod.google.com [10.243.19.143]) by wpaz21.hot.corp.google.com with ESMTP id n91Ki6cL031711 for ; Thu, 1 Oct 2009 13:49:03 -0700 Received: by pzk15 with SMTP id 15so545744pzk.3 for ; Thu, 01 Oct 2009 13:49:03 -0700 (PDT) Date: Thu, 1 Oct 2009 13:49:00 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH 30/31] Fix use of uninitialized variable in cache_grow() In-Reply-To: <1254406257-16735-1-git-send-email-sjayaraman@suse.de> Message-ID: References: <1254406257-16735-1-git-send-email-sjayaraman@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Suresh Jayaraman Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, Neil Brown , Miklos Szeredi , Wouter Verhelst , Peter Zijlstra , trond.myklebust@fys.uio.no List-ID: On Thu, 1 Oct 2009, Suresh Jayaraman wrote: > From: Miklos Szeredi > > This fixes a bug in reserve-slub.patch. > > If cache_grow() was called with objp != NULL then the 'reserve' local > variable wasn't initialized. This resulted in ac->reserve being set to > a rubbish value. Due to this in some circumstances huge amounts of > slab pages were allocated (due to slab_force_alloc() returning true), > which caused atomic page allocation failures and slowdown of the > system. > > Signed-off-by: Miklos Szeredi > Signed-off-by: Suresh Jayaraman > --- > mm/slab.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > Index: mmotm/mm/slab.c > =================================================================== > --- mmotm.orig/mm/slab.c > +++ mmotm/mm/slab.c > @@ -2760,7 +2760,7 @@ static int cache_grow(struct kmem_cache > size_t offset; > gfp_t local_flags; > struct kmem_list3 *l3; > - int reserve; > + int reserve = -1; > > /* > * Be lazy and only check for valid flags here, keeping it out of the > @@ -2816,7 +2816,8 @@ static int cache_grow(struct kmem_cache > if (local_flags & __GFP_WAIT) > local_irq_disable(); > check_irq_off(); > - slab_set_reserve(cachep, reserve); > + if (reserve != -1) > + slab_set_reserve(cachep, reserve); > spin_lock(&l3->list_lock); > > /* Make slab active. */ Given the patch description, shouldn't this be a test for objp != NULL instead, then? If so, it doesn't make sense because reserve will only be initialized when objp == NULL in the call to kmem_getpages() from cache_grow(). The title of the patch suggests this is just dealing with an uninitialized auto variable so the anticipated change would be from "int reserve" to "int uninitialized_var(result)". -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org