• Vladimir Davydov's avatar
    mem-hotplug: implement get/put_online_mems · bfc8c901
    Vladimir Davydov authored
    kmem_cache_{create,destroy,shrink} need to get a stable value of
    cpu/node online mask, because they init/destroy/access per-cpu/node
    kmem_cache parts, which can be allocated or destroyed on cpu/mem
    hotplug.  To protect against cpu hotplug, these functions use
    {get,put}_online_cpus.  However, they do nothing to synchronize with
    memory hotplug - taking the slab_mutex does not eliminate the
    possibility of race as described in patch 2.
    
    What we need there is something like get_online_cpus, but for memory.
    We already have lock_memory_hotplug, which serves for the purpose, but
    it's a bit of a hammer right now, because it's backed by a mutex.  As a
    result, it imposes some limitations to locking order, which are not
    desirable, and can't be used just like get_online_cpus.  That's why in
    patch 1 I substitute it with get/put_online_mems, which work exactly
    like get/put_online_cpus except they block not cpu, but memory hotplug.
    
    [ v1 can be found at https://lkml.org/lkml/2014/4/6/68.  I NAK'ed it by
      myself, because it used an rw semaphore for get/put_online_mems,
      making them dead lock prune.  ]
    
    This patch (of 2):
    
    {un}lock_memory_hotplug, which is used to synchronize against memory
    hotplug, is currently backed by a mutex, which makes it a bit of a
    hammer - threads that only want to get a stable value of online nodes
    mask won't be able to proceed concurrently.  Also, it imposes some
    strong locking ordering rules on it, which narrows down the set of its
    usage scenarios.
    
    This patch introduces get/put_online_mems, which are the same as
    get/put_online_cpus, but for memory hotplug, i.e.  executing a code
    inside a get/put_online_mems section will guarantee a stable value of
    online nodes, present pages, etc.
    
    lock_memory_hotplug()/unlock_memory_hotplug() are removed altogether.
    Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Tang Chen <tangchen@cn.fujitsu.com>
    Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
    Cc: Toshi Kani <toshi.kani@hp.com>
    Cc: Xishi Qiu <qiuxishi@huawei.com>
    Cc: Jiang Liu <liuj97@gmail.com>
    Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Wen Congyang <wency@cn.fujitsu.com>
    Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    bfc8c901
memory-failure.c 46.3 KB