From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f200.google.com (mail-wj0-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id AFFE66B0069 for ; Thu, 1 Dec 2016 02:02:16 -0500 (EST) Received: by mail-wj0-f200.google.com with SMTP id bk3so36838835wjc.4 for ; Wed, 30 Nov 2016 23:02:16 -0800 (PST) Received: from mail-wm0-f68.google.com (mail-wm0-f68.google.com. [74.125.82.68]) by mx.google.com with ESMTPS id z84si10830823wmg.75.2016.11.30.23.02.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 30 Nov 2016 23:02:15 -0800 (PST) Received: by mail-wm0-f68.google.com with SMTP id a20so32727779wme.2 for ; Wed, 30 Nov 2016 23:02:15 -0800 (PST) Date: Thu, 1 Dec 2016 08:02:13 +0100 From: Michal Hocko Subject: Re: [Bug 189181] New: BUG: unable to handle kernel NULL pointer dereference in mem_cgroup_node_nr_lru_pages Message-ID: <20161201070213.GA18272@dhcp22.suse.cz> References: <20161129145654.c48bebbd684edcd6f64a03fe@linux-foundation.org> <20161130170040.GJ18432@dhcp22.suse.cz> <20161130181653.GA30558@cmpxchg.org> <20161130183016.GO18432@dhcp22.suse.cz> <20161201022454.GB21693@mail-personal> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20161201022454.GB21693@mail-personal> Sender: owner-linux-mm@kvack.org List-ID: To: Marek =?iso-8859-1?Q?Marczykowski-G=F3recki?= Cc: Johannes Weiner , Andrew Morton , Mel Gorman , bugzilla-daemon@bugzilla.kernel.org, linux-mm@kvack.org, Vladimir Davydov On Thu 01-12-16 03:24:54, Marek Marczykowski-Gorecki wrote: > On Wed, Nov 30, 2016 at 07:30:17PM +0100, Michal Hocko wrote: > > On Wed 30-11-16 13:16:53, Johannes Weiner wrote: > > > Hi Michael, > > > > > > On Wed, Nov 30, 2016 at 06:00:40PM +0100, Michal Hocko wrote: > > [...] > > > > diff --git a/mm/workingset.c b/mm/workingset.c > > > > index 617475f529f4..0f07522c5c0e 100644 > > > > --- a/mm/workingset.c > > > > +++ b/mm/workingset.c > > > > @@ -348,7 +348,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker, > > > > shadow_nodes = list_lru_shrink_count(&workingset_shadow_nodes, sc); > > > > local_irq_enable(); > > > > > > > > - if (memcg_kmem_enabled()) { > > > > + if (memcg_kmem_enabled() && sc->memcg) { > > > > pages = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid, > > > > LRU_ALL_FILE); > > > > } else { > > > > > > If we do that, I'd remove the racy memcg_kmem_enabled() check > > > altogether and just check for whether we have a memcg or not. > > > > But that would make this a memcg aware shrinker even when kmem is not > > enabled... > > > > But now that I am looking into the code > > shrink_slab: > > if (memcg_kmem_enabled() && > > !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) > > continue; > > > > this should be taken care of already. So sc->memcg should be indeed > > sufficient. So unless I am missing something I will respin my local > > patch and post it later after the reporter has some time to test the > > current one. > > The above patch seems to help. At least the problem haven't occurred for > the last ~40 VM startups. I will consider this as Tested-by: Marek Marczykowski-Gorecki OK? Thanks for the report and testing! -- Michal Hocko SUSE Labs -- 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