Re: [Xen-devel] [PATCH] cpufreq/ondemand: fix race while offlining CPU

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Mar 09, 2018 at 02:34:32AM -0700, Jan Beulich wrote:
> Offlining a CPU involves stopping the cpufreq governor. The on-demand
> governor will kill the timer before letting generic code proceed, but
> since that generally isn't happening on the subject CPU,
> cpufreq_dbs_timer_resume() may run in parallel. If that managed to
> invoke the timer handler, that handler needs to run to completion before
> dbs_timer_exit() may safely exit.
> 
> Make the "stoppable" field a tristate, changing it from +1 to -1 around
> the timer function invocation, and make dbs_timer_exit() wait for it to
> become non-negative (still writing zero if it's +1).
> 
> Also adjust coding style in cpufreq_dbs_timer_resume().
> 
> Reported-by: Martin Cerveny <martin@xxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tested-by: Martin Cerveny <martin@xxxxxxxxx>

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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