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authorSilas Boyd-Wickizer <sbw@mit.edu>2012-08-03 12:34:50 -0700
committerViresh Kumar <viresh.kumar@linaro.org>2012-10-03 14:19:35 +0530
commit517ddd9e74294e42166161114226f3315c8d1376 (patch)
tree7a798f7115448ae32a2b8ed954197cd0d9da4aaf
parentf7210fc689de3ce5c3384591afeb54ead0f28699 (diff)
downloadvexpress-lsk-517ddd9e74294e42166161114226f3315c8d1376.tar.gz
Use get_online_cpus to avoid races involving CPU hotplug
If arch/x86/kernel/cpuid.c is a module, a CPU might offline or online between the for_each_online_cpu() loop and the call to register_hotcpu_notifier in cpuid_init or the call to unregister_hotcpu_notifier in cpuid_exit. The potential races can lead to leaks/duplicates, attempts to destroy non-existant devices, or random pointer dereferences. For example, in cpuid_exit if: for_each_online_cpu(cpu) cpuid_device_destroy(cpu); class_destroy(cpuid_class); __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); <----- CPU onlines unregister_hotcpu_notifier(&cpuid_class_cpu_notifier); the hotcpu notifier will attempt to create a device for the cpuid_class, which the module already destroyed. 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>
-rw-r--r--arch/x86/kernel/cpuid.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c
index 39472dd2323..60c78917190 100644
--- a/arch/x86/kernel/cpuid.c
+++ b/arch/x86/kernel/cpuid.c
@@ -199,12 +199,14 @@ static int __init cpuid_init(void)
goto out_chrdev;
}
cpuid_class->devnode = cpuid_devnode;
+ get_online_cpus();
for_each_online_cpu(i) {
err = cpuid_device_create(i);
if (err != 0)
goto out_class;
}
register_hotcpu_notifier(&cpuid_class_cpu_notifier);
+ put_online_cpus();
err = 0;
goto out;
@@ -214,6 +216,7 @@ out_class:
for_each_online_cpu(i) {
cpuid_device_destroy(i);
}
+ put_online_cpus();
class_destroy(cpuid_class);
out_chrdev:
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
@@ -225,11 +228,13 @@ static void __exit cpuid_exit(void)
{
int cpu = 0;
+ get_online_cpus();
for_each_online_cpu(cpu)
cpuid_device_destroy(cpu);
class_destroy(cpuid_class);
__unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
unregister_hotcpu_notifier(&cpuid_class_cpu_notifier);
+ put_online_cpus();
}
module_init(cpuid_init);