Messages in this thread | | | Subject | Re: [PATCH 0/2] Protect cpu map updates from ACPI processor | From | Toshi Kani <> | Date | Mon, 12 Aug 2013 18:55:03 -0600 |
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On Tue, 2013-08-13 at 02:43 +0200, Rafael J. Wysocki wrote: > On Monday, August 12, 2013 09:45:52 AM Toshi Kani wrote: > > CPU system maps are protected with reader/writer locks. The reader > > lock, put_online_cpus(), assures that the maps are not updated while > > holding the lock. The writer lock, cpu_hotplug_begin(), is used to > > udpate the cpu maps along with cpu_maps_update_begin(). > > > > However, the ACPI processor handler updates the cpu maps without > > holding the the writer lock. This patchset fixes this problem. > > > > --- > > The patchset is based on linux-next of the pm tree. > > Basically looks OK to me, but I'd just merge the patches together, > because the [2/2] is the very reason for the change made by [1/2].
I separated for reviewing purpose, but yes, they can be together. Let me know if you need me to re-send it together.
> Also it would be good to mention the actual scenario that may lead > to problems with that.
For example, the get_online_cpus() below is supposed to assure that cpu_possible_mask is not changed while the code is iterating with for_each_possible_cpu().
get_online_cpus(); for_each_possible_cpu(cpu) { : } put_online_cpus();
However, this lock has no protection with CPU hotplug since the ACPI processor handler does not use the writer lock when it updates cpu_possible_mask. The reader lock does not serialize within the readers.
Thanks, -Toshi
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