On 05/22/2014 02:53 PM, Borislav Petkov wrote:
> From: Borislav Petkov <[email protected]>
>
> So 009f225ef050 ("powercap, intel-rapl: Fix CPU hotplug callback
> registration") says how get_/put_online_cpus() should be replaced with
> this cpu_notifier_register_begin/_done().
>
> But they're still there so what's up?
>
Ok, so I retained that because the comments in the code said that
the caller of rapl_cleanup_data() should hold the hotplug lock.
Here is the snippet from the patch's changelog:
...
Fix the intel-rapl code in the powercap driver by using this latter form
of callback registration. But retain the calls to get/put_online_cpus(),
since they also protect the function rapl_cleanup_data(). By nesting
get/put_online_cpus() *inside* cpu_notifier_register_begin/done(), we avoid
the ABBA deadlock possibility mentioned above.
But looking closer at the code, I think the only requirement is that
rapl_cleanup_data() should be protected against CPU hotplug, and we
don't actually need to hold the cpu_hotplug.lock per-se.
cpu_notifier_register_begin()/end() also provide equivalent protection
against CPU hotplug. So we should be able to remove the get/put_online_cpus()
from intel-rapl driver.
Jacob/Srinivas, is the above assumption correct for rapl?
Regards,
Srivatsa S. Bhat
> Let me do what was supposed to be done.
>
> Cc: Srinivas Pandruvada <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Jacob Pan <[email protected]>
> Cc: Srivatsa S. Bhat <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Signed-off-by: Borislav Petkov <[email protected]>
> ---
> drivers/powercap/intel_rapl.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/drivers/powercap/intel_rapl.c b/drivers/powercap/intel_rapl.c
> index d9a0770b6c73..9055f3df1f64 100644
> --- a/drivers/powercap/intel_rapl.c
> +++ b/drivers/powercap/intel_rapl.c
> @@ -1377,8 +1377,6 @@ static int __init rapl_init(void)
>
> cpu_notifier_register_begin();
>
> - /* prevent CPU hotplug during detection */
> - get_online_cpus();
> ret = rapl_detect_topology();
> if (ret)
> goto done;
> @@ -1390,7 +1388,6 @@ static int __init rapl_init(void)
> }
> __register_hotcpu_notifier(&rapl_cpu_notifier);
> done:
> - put_online_cpus();
> cpu_notifier_register_done();
>
> return ret;
>
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