On Sat, 12 Aug 2017, Vladimir Davydov wrote:
> 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:
> [<ffffffff9591d28a>] kmemleak_alloc+0x4a/0xa0
> [<ffffffff9527a378>] __kmalloc_track_caller+0x148/0x2c0
> [<ffffffff95499466>] kvasprintf+0x66/0xd0
> [<ffffffff954995a9>] kasprintf+0x49/0x70
> [<ffffffff952305c6>] memcg_create_kmem_cache+0xe6/0x160
> [<ffffffff9528eaf0>] memcg_kmem_cache_create_func+0x20/0x110
> [<ffffffff950cd6c5>] process_one_work+0x205/0x5d0
> [<ffffffff950cdade>] worker_thread+0x4e/0x3a0
> [<ffffffff950d5169>] kthread+0x109/0x140
> [<ffffffff9592b8fa>] ret_from_fork+0x2a/0x40
> [<ffffffffffffffff>] 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:
> [<ffffffff9591d28a>] kmemleak_alloc+0x4a/0xa0
> [<ffffffff95275bc8>] kmem_cache_alloc+0x128/0x280
> [<ffffffff9522fedb>] create_cache+0x3b/0x1e0
> [<ffffffff952305f8>] memcg_create_kmem_cache+0x118/0x160
> [<ffffffff9528eaf0>] memcg_kmem_cache_create_func+0x20/0x110
> [<ffffffff950cd6c5>] process_one_work+0x205/0x5d0
> [<ffffffff950cdade>] worker_thread+0x4e/0x3a0
> [<ffffffff950d5169>] kthread+0x109/0x140
> [<ffffffff9592b8fa>] ret_from_fork+0x2a/0x40
> [<ffffffffffffffff>] 0xffffffffffffffff
>
> Fix the leak by adding the missing call to kobject_put() to
> sysfs_slab_remove_workfn().
>
> Signed-off-by: Vladimir Davydov <vdavydov....@gmail.com>
> Reported-and-tested-by: Andrei Vagin <ava...@gmail.com>
> Acked-by: Tejun Heo <t...@kernel.org>
> Cc: Michal Hocko <mho...@kernel.org>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Christoph Lameter <c...@linux.com>
> Cc: Pekka Enberg <penb...@kernel.org>
> Cc: David Rientjes <rient...@google.com>
> Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
> Fixes: 3b7b314053d02 ("slub: make sysfs file removal asynchronous")
Acked-by: David Rientjes <rient...@google.com>
