• Thomas Gleixner's avatar
    slub/memcg: cure the brainless abuse of sysfs attributes · 478fe303
    Thomas Gleixner authored
    memcg_propagate_slab_attrs() abuses the sysfs attribute file functions
    to propagate settings from the root kmem_cache to a newly created
    kmem_cache.  It does that with:
    
         attr->show(root, buf);
         attr->store(new, buf, strlen(bug);
    
    Aside of being a lazy and absurd hackery this is broken because it does
    not check the return value of the show() function.
    
    Some of the show() functions return 0 w/o touching the buffer.  That
    means in such a case the store function is called with the stale content
    of the previous show().  That causes nonsense like invoking
    kmem_cache_shrink() on a newly created kmem_cache.  In the worst case it
    would cause handing in an uninitialized buffer.
    
    This should be rewritten proper by adding a propagate() callback to
    those slub_attributes which must be propagated and avoid that insane
    conversion to and from ASCII, but that's too large for a hot fix.
    
    Check at least the return value of the show() function, so calling
    store() with stale content is prevented.
    
    Steven said:
     "It can cause a deadlock with get_online_cpus() that has been uncovered
      by recent cpu hotplug and lockdep changes that Thomas and Peter have
      been doing.
    
         Possible unsafe locking scenario:
    
               CPU0                    CPU1
               ----                    ----
          lock(cpu_hotplug.lock);
                                       lock(slab_mutex);
                                       lock(cpu_hotplug.lock);
          lock(slab_mutex);
    
         *** DEADLOCK ***"
    
    Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1705201244540.2255@nanosSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reported-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    478fe303
slub.c 140 KB