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Rafael J. Wysocki authored
Commit b81ea1b5 (PM / QoS: Fix concurrency issues and memory leaks in device PM QoS) put calls to pm_qos_sysfs_add_latency(), pm_qos_sysfs_add_flags(), pm_qos_sysfs_remove_latency(), and pm_qos_sysfs_remove_flags() under dev_pm_qos_mtx, which was a mistake, because it may lead to deadlocks in some situations. For example, if pm_qos_remote_wakeup_store() is run in parallel with dev_pm_qos_constraints_destroy(), they may deadlock in the following way: ====================================================== [ INFO: possible circular locking dependency detected ] 3.9.0-rc4-next-20130328-sasha-00014-g91a3267 #319 Tainted: G W ------------------------------------------------------- trinity-child6/12371 is trying to acquire lock: (s_active#54){++++.+}, at: [<ffffffff81301631>] sysfs_addrm_finish+0x31/0x60 but task is already holding lock: (dev_pm_qos_mtx){+.+.+.}, at: [<ffffffff81f07cc3>] dev_pm_qos_constraints_destroy+0x23/0x250 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (dev_pm_qos_mtx){+.+.+.}: [<ffffffff811811da>] lock_acquire+0x1aa/0x240 [<ffffffff83dab809>] __mutex_lock_common+0x59/0x5e0 [<ffffffff83dabebf>] mutex_lock_nested+0x3f/0x50 [<ffffffff81f07f2f>] dev_pm_qos_update_flags+0x3f/0xc0 [<ffffffff81f05f4f>] pm_qos_remote_wakeup_store+0x3f/0x70 [<ffffffff81efbb43>] dev_attr_store+0x13/0x20 [<ffffffff812ffdaa>] sysfs_write_file+0xfa/0x150 [<ffffffff8127f2c1>] __kernel_write+0x81/0x150 [<ffffffff812afc2d>] write_pipe_buf+0x4d/0x80 [<ffffffff812af57c>] splice_from_pipe_feed+0x7c/0x120 [<ffffffff812afa25>] __splice_from_pipe+0x45/0x80 [<ffffffff812b14fc>] splice_from_pipe+0x4c/0x70 [<ffffffff812b1538>] default_file_splice_write+0x18/0x30 [<ffffffff812afae3>] do_splice_from+0x83/0xb0 [<ffffffff812afb2e>] direct_splice_actor+0x1e/0x20 [<ffffffff812b0277>] splice_direct_to_actor+0xe7/0x200 [<ffffffff812b15bc>] do_splice_direct+0x4c/0x70 [<ffffffff8127eda9>] do_sendfile+0x169/0x300 [<ffffffff8127ff94>] SyS_sendfile64+0x64/0xb0 [<ffffffff83db7d18>] tracesys+0xe1/0xe6 -> #0 (s_active#54){++++.+}: [<ffffffff811800cf>] __lock_acquire+0x15bf/0x1e50 [<ffffffff811811da>] lock_acquire+0x1aa/0x240 [<ffffffff81300aa2>] sysfs_deactivate+0x122/0x1a0 [<ffffffff81301631>] sysfs_addrm_finish+0x31/0x60 [<ffffffff812ff77f>] sysfs_hash_and_remove+0x7f/0xb0 [<ffffffff813035a1>] sysfs_unmerge_group+0x51/0x70 [<ffffffff81f068f4>] pm_qos_sysfs_remove_flags+0x14/0x20 [<ffffffff81f07490>] __dev_pm_qos_hide_flags+0x30/0x70 [<ffffffff81f07cd5>] dev_pm_qos_constraints_destroy+0x35/0x250 [<ffffffff81f06931>] dpm_sysfs_remove+0x11/0x50 [<ffffffff81efcf6f>] device_del+0x3f/0x1b0 [<ffffffff81efd128>] device_unregister+0x48/0x60 [<ffffffff82d4083c>] usb_hub_remove_port_device+0x1c/0x20 [<ffffffff82d2a9cd>] hub_disconnect+0xdd/0x160 [<ffffffff82d36ab7>] usb_unbind_interface+0x67/0x170 [<ffffffff81f001a7>] __device_release_driver+0x87/0xe0 [<ffffffff81f00559>] device_release_driver+0x29/0x40 [<ffffffff81effc58>] bus_remove_device+0x148/0x160 [<ffffffff81efd07f>] device_del+0x14f/0x1b0 [<ffffffff82d344f9>] usb_disable_device+0xf9/0x280 [<ffffffff82d34ff8>] usb_set_configuration+0x268/0x840 [<ffffffff82d3a7fc>] usb_remove_store+0x4c/0x80 [<ffffffff81efbb43>] dev_attr_store+0x13/0x20 [<ffffffff812ffdaa>] sysfs_write_file+0xfa/0x150 [<ffffffff8127f71d>] do_loop_readv_writev+0x4d/0x90 [<ffffffff8127f999>] do_readv_writev+0xf9/0x1e0 [<ffffffff8127faba>] vfs_writev+0x3a/0x60 [<ffffffff8127fc60>] SyS_writev+0x50/0xd0 [<ffffffff83db7d18>] tracesys+0xe1/0xe6 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(dev_pm_qos_mtx); lock(s_active#54); lock(dev_pm_qos_mtx); lock(s_active#54); *** DEADLOCK *** To avoid that, remove the calls to functions mentioned above from under dev_pm_qos_mtx and introduce a separate lock to prevent races between functions that add or remove device PM QoS sysfs attributes from happening. Reported-by:
Sasha Levin <sasha.levin@oracle.com> Signed-off-by:
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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