1. 01 2月, 2017 14 次提交
  2. 31 1月, 2017 9 次提交
  3. 30 1月, 2017 9 次提交
  4. 29 1月, 2017 7 次提交
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    • D
      percpu-refcount: fix reference leak during percpu-atomic transition · 966d2b04
      Douglas Miller 提交于
      percpu_ref_tryget() and percpu_ref_tryget_live() should return
      "true" IFF they acquire a reference. But the return value from
      atomic_long_inc_not_zero() is a long and may have high bits set,
      e.g. PERCPU_COUNT_BIAS, and the return value of the tryget routines
      is bool so the reference may actually be acquired but the routines
      return "false" which results in a reference leak since the caller
      assumes it does not need to do a corresponding percpu_ref_put().
      
      This was seen when performing CPU hotplug during I/O, as hangs in
      blk_mq_freeze_queue_wait where percpu_ref_kill (blk_mq_freeze_queue_start)
      raced with percpu_ref_tryget (blk_mq_timeout_work).
      Sample stack trace:
      
      __switch_to+0x2c0/0x450
      __schedule+0x2f8/0x970
      schedule+0x48/0xc0
      blk_mq_freeze_queue_wait+0x94/0x120
      blk_mq_queue_reinit_work+0xb8/0x180
      blk_mq_queue_reinit_prepare+0x84/0xa0
      cpuhp_invoke_callback+0x17c/0x600
      cpuhp_up_callbacks+0x58/0x150
      _cpu_up+0xf0/0x1c0
      do_cpu_up+0x120/0x150
      cpu_subsys_online+0x64/0xe0
      device_online+0xb4/0x120
      online_store+0xb4/0xc0
      dev_attr_store+0x68/0xa0
      sysfs_kf_write+0x80/0xb0
      kernfs_fop_write+0x17c/0x250
      __vfs_write+0x6c/0x1e0
      vfs_write+0xd0/0x270
      SyS_write+0x6c/0x110
      system_call+0x38/0xe0
      
      Examination of the queue showed a single reference (no PERCPU_COUNT_BIAS,
      and __PERCPU_REF_DEAD, __PERCPU_REF_ATOMIC set) and no requests.
      However, conditions at the time of the race are count of PERCPU_COUNT_BIAS + 0
      and __PERCPU_REF_DEAD and __PERCPU_REF_ATOMIC set.
      
      The fix is to make the tryget routines use an actual boolean internally instead
      of the atomic long result truncated to a int.
      
      Fixes: e625305b percpu-refcount: make percpu_ref based on longs instead of ints
      Link: https://bugzilla.kernel.org/show_bug.cgi?id=190751Signed-off-by: NDouglas Miller <dougmill@linux.vnet.ibm.com>
      Reviewed-by: NJens Axboe <axboe@fb.com>
      Signed-off-by: NTejun Heo <tj@kernel.org>
      Fixes: e625305b ("percpu-refcount: make percpu_ref based on longs instead of ints")
      Cc: stable@vger.kernel.org # v3.18+
      966d2b04