Re: [PATCH] slab: store tagged freelist for off-slab slabmgmt

From: Andrey Konovalov <andreyknvl@google.com>
To: Qian Cai <cai@lca.pw>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	 Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	 Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	 Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	 kasan-dev <kasan-dev@googlegroups.com>,
	 Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] slab: store tagged freelist for off-slab slabmgmt
Date: Wed, 3 Apr 2019 18:39:30 +0200	[thread overview]
Message-ID: <CAAeHK+wB4L9nj+iPf8iHUbuWBCE_FQN4aea4zswEd4bbr49FPQ@mail.gmail.com> (raw)
In-Reply-To: <1554296870.26196.32.camel@lca.pw>

On Wed, Apr 3, 2019 at 3:07 PM Qian Cai <cai@lca.pw> wrote:
>
> On Wed, 2019-04-03 at 13:23 +0200, Andrey Konovalov wrote:
> > On Wed, Apr 3, 2019 at 4:29 AM Qian Cai <cai@lca.pw> wrote:
> > >
> > > The commit 51dedad06b5f ("kasan, slab: make freelist stored without
> > > tags") calls kasan_reset_tag() for off-slab slab management object
> > > leading to freelist being stored non-tagged. However, cache_grow_begin()
> > > -> alloc_slabmgmt() -> kmem_cache_alloc_node() which assigns a tag for
> > > the address and stores in the shadow address. As the result, it causes
> > > endless errors below during boot due to drain_freelist() ->
> > > slab_destroy() -> kasan_slab_free() which compares already untagged
> > > freelist against the stored tag in the shadow address. Since off-slab
> > > slab management object freelist is such a special case, so just store it
> > > tagged. Non-off-slab management object freelist is still stored untagged
> > > which has not been assigned a tag and should not cause any other
> > > troubles with this inconsistency.
> >
> > Hi Qian,
> >
> > Could you share the config (or other steps) you used to reproduce this?
>
> https://git.sr.ht/~cai/linux-debug/blob/master/config
>
> Additional command-line option to boot:
>
> page_poison=on crashkernel=768M earlycon page_owner=on numa_balancing=enable
> systemd.unified_cgroup_hierarchy=1 debug_guardpage_minorder=1

Reproduced, thanks!

As far as my understanding of how SLAB works goes, this change looks good to me.

Reviewed-by: Andrey Konovalov <andreyknvl@google.com>

Thanks, Qian!

>
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