In the Linux kernel, the following vulnerability has been resolved: mailbox: mtk-cmdq: Move devm_mbox_controller_register() after devm_pm_runtime_enable() When mtk-cmdq unbinds, a WARN_ON message with condition pm_runtime_get_sync() < 0 occurs. According to the call tracei below: cmdq_mbox_shutdown mbox_free_channel mbox_controller_unregister __devm_mbox_controller_unregister ... The root cause can be deduced to be calling pm_runtime_get_sync() after calling pm_runtime_disable() as observed below: 1. CMDQ driver uses devm_mbox_controller_register() in cmdq_probe() to bind the cmdq device to the mbox_controller, so devm_mbox_controller_unregister() will automatically unregister the device bound to the mailbox controller when the device-managed resource is removed. That means devm_mbox_controller_unregister() and cmdq_mbox_shoutdown() will be called after cmdq_remove(). 2. CMDQ driver also uses devm_pm_runtime_enable() in cmdq_probe() after devm_mbox_controller_register(), so that devm_pm_runtime_disable() will be called after cmdq_remove(), but before devm_mbox_controller_unregister(). To fix this problem, cmdq_probe() needs to move devm_mbox_controller_register() after devm_pm_runtime_enable() to make devm_pm_runtime_disable() be called after devm_mbox_controller_unregister().
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