2012-08-03 19:39:35

by Silas Boyd-Wickizer

Subject: [PATCH 3/4 V2] 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(+)

diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
index 8689664..54b01ac 100644
--- a/drivers/hwmon/via-cputemp.c
+++ b/drivers/hwmon/via-cputemp.c
@@ -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);
}

--
1.7.10.4

2012-08-04 08:52:35

by Jean Delvare

Subject: Re: [PATCH 3/4 V2] Use get_online_cpus to avoid races involving CPU hotplug

On Fri, 3 Aug 2012 12:35:28 -0700, Silas Boyd-Wickizer wrote:
> 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(+)
> (...)

Applied, thanks.

--
Jean Delvare