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Use get_online_cpus to avoid races involving CPU hotplug

PATCH Applied Silas Boyd-Wickizer 2 participants 2 messages Aug 3, 2012 – Aug 4, 2012 Hardware monitoring

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Silas Boyd-Wickizer

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PATCH v2 3/4 Use get_online_cpus to avoid races involving CPU hotplug

via_cputemp_init in drivers/hwmon/via-cputemp.c loops with for_each_online_cpu, adding platform_devices, then calls register_hotcpu_notifier. If a CPU is offlined between the loop and register_hotcpu_notifier, then later onlined, via_cputemp_device_add will attempt to add platform devices with the same ID. A similar race occurs during via_cputemp_exit, after the module calls unregister_hotcpu_notifier, a CPU might offline and a device will exist for a CPU that is offline.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier with get_online_cpus+put_online_cpus; and surrounds unregister_hotcpu_notifier and device unregistering with get_online_cpus+put_online_cpus.

Build tested.

Signed-off-by Silas Boyd-Wickizer <[email protected]>
---
 drivers/hwmon/via-cputemp.c |    5 +++++
 1 file changed, 5 insertions(+)
drivers/hwmon/via-cputemp.c +5 -0
index 8689664..54b01ac 100644
@@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
 	if (err)
 		goto exit;
 
+	get_online_cpus();
 	for_each_online_cpu(i) {
 		struct cpuinfo_x86 *c = &cpu_data(i);
 

@@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
 
 #ifndef CONFIG_HOTPLUG_CPU
 	if (list_empty(&pdev_list)) {
+		put_online_cpus();
 		err = -ENODEV;
 		goto exit_driver_unreg;
 	}
 #endif
 
 	register_hotcpu_notifier(&via_cputemp_cpu_notifier);
+	put_online_cpus();
 	return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU

@@ -367,6 +370,7 @@ static void __exit via_cputemp_exit(void)
 {
 	struct pdev_entry *p, *n;
 
+	get_online_cpus();
 	unregister_hotcpu_notifier(&via_cputemp_cpu_notifier);
 	mutex_lock(&pdev_list_mutex);
 	list_for_each_entry_safe(p, n, &pdev_list, list) {

@@ -375,6 +379,7 @@ static void __exit via_cputemp_exit(void)
 		kfree(p);
 	}
 	mutex_unlock(&pdev_list_mutex);
+	put_online_cpus();
 	platform_driver_unregister(&via_cputemp_driver);
 }
Signature · 1 line
1.7.10.4
Applied
#1 lore raw
Quoted 14 lines · Silas Boyd-Wickizer

via_cputemp_init in drivers/hwmon/via-cputemp.c loops with for_each_online_cpu, adding platform_devices, then calls register_hotcpu_notifier. If a CPU is offlined between the loop and register_hotcpu_notifier, then later onlined, via_cputemp_device_add will attempt to add platform devices with the same ID. A similar race occurs during via_cputemp_exit, after the module calls unregister_hotcpu_notifier, a CPU might offline and a device will exist for a CPU that is offline.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier with get_online_cpus+put_online_cpus; and surrounds unregister_hotcpu_notifier and device unregistering with get_online_cpus+put_online_cpus.

Quoted 7 lines

Build tested.

Signed-off-by Silas Boyd-Wickizer <[email protected]>
---
 drivers/hwmon/via-cputemp.c |    5 +++++
 1 file changed, 5 insertions(+)

(...)

Applied, thanks.

Signature · 1 line
Jean Delvare