From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Konrad Rzeszutek Wilk , "Rafael J. Wysocki" Subject: [PATCH 3.12 44/62] cpuidle: Check for dev before deregistering it. Date: Tue, 10 Dec 2013 00:01:15 -0800 Message-Id: <20131210080100.519816217@linuxfoundation.org> In-Reply-To: <20131210080057.415644748@linuxfoundation.org> References: <20131210080057.415644748@linuxfoundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Konrad Rzeszutek Wilk commit 813e8e3d6aaa0b511126cce15c16a931afffe768 upstream. If not, we could end up in the unfortunate situation where we dereference a NULL pointer b/c we have cpuidle disabled. This is the case when booting under Xen (which uses the ACPI P/C states but disables the CPU idle driver) - and can be easily reproduced when booting with cpuidle.off=1. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [] cpuidle_unregister_device+0x2a/0x90 .. snip.. Call Trace: [] acpi_processor_power_exit+0x3c/0x5c [] acpi_processor_stop+0x61/0xb6 [] __device_release_driver+0fffff81421653>] device_release_driver+0x23/0x30 [] bus_remove_device+0x108/0x180 [] device_del+0x129/0x1c0 [] ? unregister_xenbus_watch+0x1f0/0x1f0 [] device_unregister+0x1e/0x60 [] unregister_cpu+0x39/0x60 [] arch_unregister_cpu+0x23/0x30 [] handle_vcpu_hotplug_event+0xc1/0xe0 [] xenwatch_thread+0x45/0x120 [] ? abort_exclusive_wait+0xb0/0xb0 [] kthread+0xd2/0xf0 [] ? kthread_create_on_node+0x180/0x180 [] ret_from_fork+0x7c/0xb0 [] ? kthread_create_on_node+0x180/0x180 This problem also appears in 3.12 and could be a candidate for backport. Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman --- drivers/cpuidle/cpuidle.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -448,7 +448,7 @@ EXPORT_SYMBOL_GPL(cpuidle_register_devic */ void cpuidle_unregister_device(struct cpuidle_device *dev) { - if (dev->registered == 0) + if (!dev || dev->registered == 0) return; cpuidle_pause_and_lock();