• Vladimir Davydov's avatar
    slub: fix per memcg cache leak on css offline · f6ba4880
    Vladimir Davydov authored
    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: 3b7b3140
    
     ("slub: make sysfs file removal asynchronous")
    Signed-off-by: default avatarVladimir Davydov <vdavydov.dev@gmail.com>
    Reported-by: default avatarAndrei Vagin <avagin@gmail.com>
    Tested-by: default avatarAndrei Vagin <avagin@gmail.com>
    Acked-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: <stable@vger.kernel.org>	[4.12.x]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f6ba4880