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| author | Silas Boyd-Wickizer <sbw@mit.edu> | 2012-08-03 12:34:50 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2012-09-23 07:43:56 -0700 |
| commit | 429227bbe55647aa42f8f63cac61e4544e248629 (patch) | |
| tree | 345535746085ed30bfea14e38e23c61a540ddbbd | |
| parent | a2db672aa305a045404615e5222ba681bab6cf58 (diff) | |
| download | linux-429227bbe55647aa42f8f63cac61e4544e248629.tar.bz2 | |
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>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | arch/x86/kernel/cpuid.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c index 39472dd2323f..60c78917190c 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); |