1. 29 Aug, 2013 1 commit
    • Rafael J. Wysocki's avatar
      driver core / ACPI: Avoid device hot remove locking issues · 5e33bc41
      Rafael J. Wysocki authored
      device_hotplug_lock is held around the acpi_bus_trim() call in
      acpi_scan_hot_remove() which generally removes devices (it removes
      ACPI device objects at least, but it may also remove "physical"
      device objects through .detach() callbacks of ACPI scan handlers).
      Thus, potentially, device sysfs attributes are removed under that
      lock and to remove those attributes it is necessary to hold the
      s_active references of their directory entries for writing.
      
      On the other hand, the execution of a .show() or .store() callback
      from a sysfs attribute is carried out with that attribute's s_active
      reference held for reading.  Consequently, if any device sysfs
      attribute that may be removed from within acpi_scan_hot_remove()
      through acpi_bus_trim() has a .store() or .show() callback which
      acquires device_hotplug_lock, the execution of that callback may
      deadlock with the removal of the attribute.  [Unfortunately, the
      "online" device attribute of CPUs and memory blocks is one of them.]
      
      To avoid such deadlocks, make all of the sysfs attribute callbacks
      that need to lock device hotplug, for example store_online(), use
      a special function, lock_device_hotplug_sysfs(), to lock device
      hotplug and return the result of that function immediately if it is
      not zero.  This will cause the s_active reference of the directory
      entry in question to be released and the syscall to be restarted
      if device_hotplug_lock cannot be acquired.
      
      [show_online() actually doesn't need to lock device hotplug, but
      it is useful to serialize it with respect to device_offline() and
      device_online() for the same device (in case user space attempts to
      run them concurrently) which can be done with the help of
      device_lock().]
      Reported-by: default avatarYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
      Reported-and-tested-by: default avatarGu Zheng <guz.fnst@cn.fujitsu.com>
      Suggested-by: default avatarTejun Heo <tj@kernel.org>
      Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
      Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      Acked-by: default avatarToshi Kani <toshi.kani@hp.com>
      5e33bc41
  2. 26 Aug, 2013 1 commit
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