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From: Keir Fraser <keir.fraser@eu.citrix.com>
To: "Wei, Gang" <gang.wei@intel.com>,
	"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Subject: Re: [PATCH]CPUFREQ: Fix two racing issues during cpu hotplug
Date: Mon, 12 Apr 2010 07:09:39 +0100	[thread overview]
Message-ID: <C7E877B3.10596%keir.fraser@eu.citrix.com> (raw)
In-Reply-To: <E6467867A6B05E4FA831B7DF29925F5C40F16B24@shzsmsx502.ccr.corp.intel.com>

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

  reply	other threads:[~2010-04-12  6:09 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-04-12  4:45 [PATCH]CPUFREQ: Fix two racing issues during cpu hotplug Wei, Gang
2010-04-12  6:09 ` Keir Fraser [this message]
2010-04-12  6:54   ` Wei, Gang
2010-04-12  6:59     ` Keir Fraser
2010-04-12  7:40       ` Wei, Gang

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