Messages in this thread | | | Date | Fri, 24 May 2013 11:01:35 +0530 | Subject | Re: [PATCH] cpufreq: fix governor start/stop race condition | From | Viresh Kumar <> |
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On 23 May 2013 08:14, Xiaoguang Chen <chenxg@marvell.com> wrote: > Do you mean my patch will cause deadlock? I once tried to add another lock > to protect the GOV_STOP/START sequence instead of using the rwsem in this > patch. > But I saw deadlock indeed. > In cpufreq_add_policy_cpu, the lock has to be added before the rwsem since > GOV_STOP is > before lock_policy_rwsem_write, but in cpufreq_update_policy, it will first > get the rwsem, and then > call __cpufreq_set_policy which will contain GOV_STOP again, if we add the > new lock before this GOV_STOP, > then we may get deadlock in below sequence: > 1) hotplug in one cpu by calling cpufreq_add_policy_cpu in which new lock is > locked first then rwsem is locked. > 2) governor change in cpufreq_update_policy in which rwsem is locked first > then new lock is locked. > this is a deadlock issue if above two steps interleaves
Check this patch.
https://patchwork-mail.kernel.org/patch/2575231/
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