Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752305AbdHLSLj (ORCPT ); Sat, 12 Aug 2017 14:11:39 -0400 Received: from mail-lf0-f68.google.com ([209.85.215.68]:38245 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752261AbdHLSLh (ORCPT ); Sat, 12 Aug 2017 14:11:37 -0400 From: Vladimir Davydov To: Andrew Morton Cc: Michal Hocko , Johannes Weiner , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrei Vagin , Tejun Heo , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] slub: fix per memcg cache leak on css offline Date: Sat, 12 Aug 2017 21:11:34 +0300 Message-Id: <20170812181134.25027-1-vdavydov.dev@gmail.com> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3594 Lines: 86 To avoid a possible deadlock, sysfs_slab_remove() schedules an asynchronous work to delete sysfs entries corresponding to the kmem cache. To ensure the cache isn't freed before the work function is called, it takes a reference to the cache kobject. The reference is supposed to be released by the work function. However, the work function (sysfs_slab_remove_workfn()) does nothing in case the cache sysfs entry has already been deleted, leaking the kobject and the corresponding cache. This may happen on a per memcg cache destruction, because sysfs entries of a per memcg cache are deleted on memcg offline if the cache is empty (see __kmemcg_cache_deactivate()). The kmemleak report looks like this: unreferenced object 0xffff9f798a79f540 (size 32): comm "kworker/1:4", pid 15416, jiffies 4307432429 (age 28687.554s) hex dump (first 32 bytes): 6b 6d 61 6c 6c 6f 63 2d 31 36 28 31 35 39 39 3a kmalloc-16(1599: 6e 65 77 72 6f 6f 74 29 00 23 6b c0 ff ff ff ff newroot).#k..... backtrace: [] kmemleak_alloc+0x4a/0xa0 [] __kmalloc_track_caller+0x148/0x2c0 [] kvasprintf+0x66/0xd0 [] kasprintf+0x49/0x70 [] memcg_create_kmem_cache+0xe6/0x160 [] memcg_kmem_cache_create_func+0x20/0x110 [] process_one_work+0x205/0x5d0 [] worker_thread+0x4e/0x3a0 [] kthread+0x109/0x140 [] ret_from_fork+0x2a/0x40 [] 0xffffffffffffffff unreferenced object 0xffff9f79b6136840 (size 416): comm "kworker/1:4", pid 15416, jiffies 4307432429 (age 28687.573s) hex dump (first 32 bytes): 40 fb 80 c2 3e 33 00 00 00 00 00 40 00 00 00 00 @...>3.....@.... 00 00 00 00 00 00 00 00 10 00 00 00 10 00 00 00 ................ backtrace: [] kmemleak_alloc+0x4a/0xa0 [] kmem_cache_alloc+0x128/0x280 [] create_cache+0x3b/0x1e0 [] memcg_create_kmem_cache+0x118/0x160 [] memcg_kmem_cache_create_func+0x20/0x110 [] process_one_work+0x205/0x5d0 [] worker_thread+0x4e/0x3a0 [] kthread+0x109/0x140 [] ret_from_fork+0x2a/0x40 [] 0xffffffffffffffff Fix the leak by adding the missing call to kobject_put() to sysfs_slab_remove_workfn(). Signed-off-by: Vladimir Davydov Reported-and-tested-by: Andrei Vagin Acked-by: Tejun Heo Cc: Michal Hocko Cc: Johannes Weiner Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Fixes: 3b7b314053d02 ("slub: make sysfs file removal asynchronous") --- mm/slub.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/slub.c b/mm/slub.c index 364c0e769a05..0a9ee4f8dbb3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5642,13 +5642,14 @@ static void sysfs_slab_remove_workfn(struct work_struct *work) * A cache is never shut down before deactivation is * complete, so no need to worry about synchronization. */ - return; + goto out; #ifdef CONFIG_MEMCG kset_unregister(s->memcg_kset); #endif kobject_uevent(&s->kobj, KOBJ_REMOVE); kobject_del(&s->kobj); +out: kobject_put(&s->kobj); } -- 2.11.0