* [PATCH 1/4 V2] Use get_online_cpus to avoid races involving CPU hotplug
@ 2012-08-03 19:33 Silas Boyd-Wickizer
2012-08-13 16:50 ` Paul E. McKenney
0 siblings, 1 reply; 2+ messages in thread
From: Silas Boyd-Wickizer @ 2012-08-03 19:33 UTC (permalink / raw
To: linux-kernel
Cc: Paul E. McKenney, H. Peter Anvin, Thomas Gleixner, x86,
Ingo Molnar
If arch/x86/kernel/msr.c is a module, a CPU might offline or online
between the for_each_online_cpu(i) loop and the call to
register_hotcpu_notifier in msr_init or the call to
unregister_hotcpu_notifier in msr_exit. The potential races can lead
to leaks/duplicates, attempts to destroy non-existant devices, or
random pointer dereferences.
For example, in msr_init if:
for_each_online_cpu(i) {
err = msr_device_create(i);
if (err != 0)
goto out_class;
}
<----- CPU offlines
register_hotcpu_notifier(&msr_class_cpu_notifier);
and the CPU never onlines before msr_exit, then the module will never
call msr_device_destroy for the associated CPU.
This fix surrounds for_each_online_cpu and register_hotcpu_notifier or
unregister_hotcpu_notifier with get_online_cpus+put_online_cpus.
Tested on a VM.
Signed-off-by: Silas Boyd-Wickizer <sbw@mit.edu>
---
arch/x86/kernel/msr.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index eb11369..a7c5661 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -257,12 +257,14 @@ static int __init msr_init(void)
goto out_chrdev;
}
msr_class->devnode = msr_devnode;
+ get_online_cpus();
for_each_online_cpu(i) {
err = msr_device_create(i);
if (err != 0)
goto out_class;
}
register_hotcpu_notifier(&msr_class_cpu_notifier);
+ put_online_cpus();
err = 0;
goto out;
@@ -271,6 +273,7 @@ out_class:
i = 0;
for_each_online_cpu(i)
msr_device_destroy(i);
+ put_online_cpus();
class_destroy(msr_class);
out_chrdev:
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
@@ -281,11 +284,13 @@ out:
static void __exit msr_exit(void)
{
int cpu = 0;
+ get_online_cpus();
for_each_online_cpu(cpu)
msr_device_destroy(cpu);
class_destroy(msr_class);
__unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
unregister_hotcpu_notifier(&msr_class_cpu_notifier);
+ put_online_cpus();
}
module_init(msr_init);
--
1.7.10.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH 1/4 V2] Use get_online_cpus to avoid races involving CPU hotplug
2012-08-03 19:33 [PATCH 1/4 V2] Use get_online_cpus to avoid races involving CPU hotplug Silas Boyd-Wickizer
@ 2012-08-13 16:50 ` Paul E. McKenney
0 siblings, 0 replies; 2+ messages in thread
From: Paul E. McKenney @ 2012-08-13 16:50 UTC (permalink / raw
To: Silas Boyd-Wickizer
Cc: linux-kernel, H. Peter Anvin, Thomas Gleixner, x86, Ingo Molnar
On Fri, Aug 03, 2012 at 12:33:27PM -0700, Silas Boyd-Wickizer wrote:
> If arch/x86/kernel/msr.c is a module, a CPU might offline or online
> between the for_each_online_cpu(i) loop and the call to
> register_hotcpu_notifier in msr_init or the call to
> unregister_hotcpu_notifier in msr_exit. The potential races can lead
> to leaks/duplicates, attempts to destroy non-existant devices, or
> random pointer dereferences.
>
> For example, in msr_init if:
>
> for_each_online_cpu(i) {
> err = msr_device_create(i);
> if (err != 0)
> goto out_class;
> }
> <----- CPU offlines
> register_hotcpu_notifier(&msr_class_cpu_notifier);
>
> and the CPU never onlines before msr_exit, then the module will never
> call msr_device_destroy for the associated CPU.
>
> This fix surrounds for_each_online_cpu and register_hotcpu_notifier or
> unregister_hotcpu_notifier with get_online_cpus+put_online_cpus.
>
> Tested on a VM.
>
> Signed-off-by: Silas Boyd-Wickizer <sbw@mit.edu>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> arch/x86/kernel/msr.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
> index eb11369..a7c5661 100644
> --- a/arch/x86/kernel/msr.c
> +++ b/arch/x86/kernel/msr.c
> @@ -257,12 +257,14 @@ static int __init msr_init(void)
> goto out_chrdev;
> }
> msr_class->devnode = msr_devnode;
> + get_online_cpus();
> for_each_online_cpu(i) {
> err = msr_device_create(i);
> if (err != 0)
> goto out_class;
> }
> register_hotcpu_notifier(&msr_class_cpu_notifier);
> + put_online_cpus();
>
> err = 0;
> goto out;
> @@ -271,6 +273,7 @@ out_class:
> i = 0;
> for_each_online_cpu(i)
> msr_device_destroy(i);
> + put_online_cpus();
> class_destroy(msr_class);
> out_chrdev:
> __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
> @@ -281,11 +284,13 @@ out:
> static void __exit msr_exit(void)
> {
> int cpu = 0;
> + get_online_cpus();
> for_each_online_cpu(cpu)
> msr_device_destroy(cpu);
> class_destroy(msr_class);
> __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr");
> unregister_hotcpu_notifier(&msr_class_cpu_notifier);
> + put_online_cpus();
> }
>
> module_init(msr_init);
> --
> 1.7.10.4
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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