Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] slab, slub: skip unnecessary kasan_cache_shutdown()
To:     Shakeel Butt <shakeelb@google.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Greg Thelen <gthelen@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20180327230603.54721-1-shakeelb@google.com>
From:   Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <3d48de97-0e5f-eba4-0d66-32eb300b79c3@virtuozzo.com>
Date:   Wed, 28 Mar 2018 20:03:20 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.7.0
MIME-Version: 1.0
In-Reply-To: <20180327230603.54721-1-shakeelb@google.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Received-SPF: None (protection.outlook.com: virtuozzo.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Mar 2018 17:02:33.1497 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 0104f618-1c11-413a-afb1-08d594cdb344
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f
X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB3253
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 03/28/2018 02:06 AM, Shakeel Butt wrote:
> The kasan quarantine is designed to delay freeing slab objects to catch
> use-after-free. The quarantine can be large (several percent of machine
> memory size). When kmem_caches are deleted related objects are flushed
> from the quarantine but this requires scanning the entire quarantine
> which can be very slow. We have seen the kernel busily working on this
> while holding slab_mutex and badly affecting cache_reaper, slabinfo
> readers and memcg kmem cache creations.
> 
> It can easily reproduced by following script:
> 
> 	yes . | head -1000000 | xargs stat > /dev/null
> 	for i in `seq 1 10`; do
> 		seq 500 | (cd /cg/memory && xargs mkdir)
> 		seq 500 | xargs -I{} sh -c 'echo $BASHPID > \
> 			/cg/memory/{}/tasks && exec stat .' > /dev/null
> 		seq 500 | (cd /cg/memory && xargs rmdir)
> 	done
> 
> The busy stack:
>     kasan_cache_shutdown
>     shutdown_cache
>     memcg_destroy_kmem_caches
>     mem_cgroup_css_free
>     css_free_rwork_fn
>     process_one_work
>     worker_thread
>     kthread
>     ret_from_fork
> 
> This patch is based on the observation that if the kmem_cache to be
> destroyed is empty then there should not be any objects of this cache in
> the quarantine.
> 
> Without the patch the script got stuck for couple of hours. With the
> patch the script completed within a second.
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> 

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>