linux-kernel - [PATCH 4.12 17/41] slub: fix per memcg cache leak on css offline

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Message-Id: <20170822190942.622984262@linuxfoundation.org>
Date:   Tue, 22 Aug 2017 12:13:45 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrei Vagin <avagin@...il.com>, Tejun Heo <tj@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.12 17/41] slub: fix per memcg cache leak on css offline

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vladimir Davydov <vdavydov.dev@...il.com>

commit f6ba488073fe8159851fe398cc3c5ee383bb4c7a upstream.

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
  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

Fix the leak by adding the missing call to kobject_put() to
sysfs_slab_remove_workfn().

Link: http://lkml.kernel.org/r/20170812181134.25027-1-vdavydov.dev@gmail.com
Fixes: 3b7b314053d02 ("slub: make sysfs file removal asynchronous")
Signed-off-by: Vladimir Davydov <vdavydov.dev@...il.com>
Reported-by: Andrei Vagin <avagin@...il.com>
Tested-by: Andrei Vagin <avagin@...il.com>
Acked-by: Tejun Heo <tj@...nel.org>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/slub.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5637,13 +5637,14 @@ static void sysfs_slab_remove_workfn(str
 		 * 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);
 }