[Xen-devel] Re: [PATCH]CPUFREQ: Fix two racing issues during cpu hotplug

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/04/2010 05:45, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:

> Move cpufreq_del_cpu() call into __cpu_disable to eliminate racing with dbs
> timer handler on policy & drv_data. Put it after local_irq_enable because
> xmalloc/xfree in cpufreq_del_cpu assert for this.

Can't you just kill_timer()? Adding extra code into a stop_machine context
is dangerous: e.g.,
xmalloc()->alloc_xenheap_pages()->memguard_unguard_range()->map_pages_to_xen
()->flush_area_all() results in deadlock as other cpus are spinning with
irqs disabled.

> Change access to cpufreq_statistic_lock from spin_lock to spin_lock_irqsave to
> avoid statistic data access racing between cpufreq_statistic_exit and dbs
> timer handler.

DBS timer handler is called in softirq context; cpu_freq_statistic_exit()
appears also always to be called from non-irq context. I don't see what
interrupt context you are protecting against.

 -- Keir



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