Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755170AbaFBODy (ORCPT ); Mon, 2 Jun 2014 10:03:54 -0400 Received: from mail-vc0-f176.google.com ([209.85.220.176]:36894 "EHLO mail-vc0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755005AbaFBODw (ORCPT ); Mon, 2 Jun 2014 10:03:52 -0400 MIME-Version: 1.0 In-Reply-To: <20140602114741.GA1039@esperanza> References: <5d2fbc894a2c62597e7196bb1ebb8357b15529ab.1401457502.git.vdavydov@parallels.com> <20140531110456.GC25076@esperanza> <20140602042435.GA17964@js1304-P5Q-DELUXE> <20140602114741.GA1039@esperanza> Date: Mon, 2 Jun 2014 23:03:51 +0900 Message-ID: Subject: Re: [PATCH -mm 7/8] slub: make dead caches discard free slabs immediately From: Joonsoo Kim To: Vladimir Davydov Cc: Joonsoo Kim , Christoph Lameter , Andrew Morton , Johannes Weiner , Michal Hocko , LKML , Linux Memory Management List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-06-02 20:47 GMT+09:00 Vladimir Davydov : > Hi Joonsoo, > > On Mon, Jun 02, 2014 at 01:24:36PM +0900, Joonsoo Kim wrote: >> On Sat, May 31, 2014 at 03:04:58PM +0400, Vladimir Davydov wrote: >> > On Fri, May 30, 2014 at 09:57:10AM -0500, Christoph Lameter wrote: >> > > On Fri, 30 May 2014, Vladimir Davydov wrote: >> > > >> > > > (3) is a bit more difficult, because slabs are added to per-cpu partial >> > > > lists lock-less. Fortunately, we only have to handle the __slab_free >> > > > case, because, as there shouldn't be any allocation requests dispatched >> > > > to a dead memcg cache, get_partial_node() should never be called. In >> > > > __slab_free we use cmpxchg to modify kmem_cache_cpu->partial (see >> > > > put_cpu_partial) so that setting ->partial to a special value, which >> > > > will make put_cpu_partial bail out, will do the trick. > [...] >> I think that we can do (3) easily. >> If we check memcg_cache_dead() in the end of put_cpu_partial() rather >> than in the begin of put_cpu_partial(), we can avoid the race you >> mentioned. If someone do put_cpu_partial() before dead flag is set, >> it can be zapped by who set dead flag. And if someone do >> put_cpu_partial() after dead flag is set, it can be zapped by who >> do put_cpu_partial(). > > After put_cpu_partial() adds a frozen slab to a per cpu partial list, > the slab becomes visible to other threads, which means it can be > unfrozen and freed. The latter can trigger cache destruction. Hence we > shouldn't touch the cache, in particular call memcg_cache_dead() on it, > after calling put_cpu_partial(), otherwise we can get use-after-free. > > However, what you propose makes sense if we disable irqs before adding a > slab to a partial list and enable them only after checking if the cache > is dead and unfreezing all partials if so, i.e. > > diff --git a/mm/slub.c b/mm/slub.c > index d96faa2464c3..14b9e9a8677c 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2030,8 +2030,15 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) > struct page *oldpage; > int pages; > int pobjects; > + unsigned long flags; > + int irq_saved = 0; > > do { > + if (irq_saved) { > + local_irq_restore(flags); > + irq_saved = 0; > + } > + > pages = 0; > pobjects = 0; > oldpage = this_cpu_read(s->cpu_slab->partial); > @@ -2062,8 +2069,16 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) > page->pobjects = pobjects; > page->next = oldpage; > > + local_irq_save(flags); > + irq_saved = 1; > + > } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) > != oldpage); > + > + if (memcg_cache_dead(s)) > + unfreeze_partials(s, this_cpu_ptr(s->cpu_slab)); > + > + local_irq_restore(flags); > #endif > } > > > That would be safe against possible cache destruction, because to remove > a slab from a per cpu partial list we have to run on the cpu it was > frozen on. Disabling irqs makes it impossible. Hmm... this is also a bit ugly. How about following change? Thanks. diff --git a/mm/slub.c b/mm/slub.c index 2b1ce69..6adab87 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2058,6 +2058,21 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage); + + if (memcg_cache_dead(s)) { + bool done = false; + unsigned long flags; + + local_irq_save(flags); + if (this_cpu_read(s->cpu_slab->partial) == page) { + done = true; + unfreeze_partials(s, this_cpu_ptr); + } + local_irq_restore(flags); + + if (!done) + flush_all(s); + } #endif } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/