Messages in this thread Patch in this message |  | | From | "Srivatsa S. Bhat" <> | Subject | [PATCH 23/51] x86, amd, uncore: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:38:50 +0530 |
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Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below:
get_online_cpus();
for_each_online_cpu(cpu) init_cpu(cpu);
register_cpu_notifier(&foobar_cpu_notifier);
put_online_cpus();
This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations).
Instead, the correct and race-free way of performing the callback registration is:
cpu_maps_update_begin();
for_each_online_cpu(cpu) init_cpu(cpu);
/* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier);
cpu_maps_update_done();
Fix the amd-uncore code in x86 by using this latter form of callback registration.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Paul Mackerras <paulus@samba.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
arch/x86/kernel/cpu/perf_event_amd_uncore.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_amd_uncore.c b/arch/x86/kernel/cpu/perf_event_amd_uncore.c index 754291a..3982ef0 100644 --- a/arch/x86/kernel/cpu/perf_event_amd_uncore.c +++ b/arch/x86/kernel/cpu/perf_event_amd_uncore.c @@ -531,15 +531,16 @@ static int __init amd_uncore_init(void) if (ret) return -ENODEV; - get_online_cpus(); + cpu_maps_update_begin(); + /* init cpus already online before registering for hotplug notifier */ for_each_online_cpu(cpu) { amd_uncore_cpu_up_prepare(cpu); smp_call_function_single(cpu, init_cpu_already_online, NULL, 1); } - register_cpu_notifier(&amd_uncore_cpu_notifier_block); - put_online_cpus(); + __register_cpu_notifier(&amd_uncore_cpu_notifier_block); + cpu_maps_update_done(); return 0; }
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