From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: tglx@linutronix.de, peterz@infradead.org,
paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au,
mingo@kernel.org, namhyung@kernel.org,
vincent.guittot@linaro.org, sbw@mit.edu, tj@kernel.org,
amit.kucheria@linaro.org, rostedt@goodmis.org, rjw@sisk.pl,
wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com,
nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly
Date: Wed, 05 Dec 2012 18:11:51 +0530 [thread overview]
Message-ID: <50BF410F.5020204@linux.vnet.ibm.com> (raw)
In-Reply-To: <20121204141707.b792e488.akpm@linux-foundation.org>
On 12/05/2012 03:47 AM, Andrew Morton wrote:
> On Tue, 04 Dec 2012 14:24:28 +0530
> "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>
>> From: Michael Wang <wangyun@linux.vnet.ibm.com>
>>
>> With stop_machine() gone from the CPU offline path, we can't depend on
>> preempt_disable() to prevent CPUs from going offline from under us.
>>
>> Use the get/put_online_cpus_stable_atomic() APIs to prevent CPUs from going
>> offline, while invoking from atomic context.
>>
>> ...
>>
>> */
>> - this_cpu = get_cpu();
>> + get_online_cpus_stable_atomic();
>> + this_cpu = smp_processor_id();
>
> I wonder if get_online_cpus_stable_atomic() should return the local CPU
> ID. Just as a little convenience thing. Time will tell.
>
With the new version which doesn't use extra cpumasks, we won't have to
bother about this..
>> /*
>> * Can deadlock when called with interrupts disabled.
>>
>> ...
>>
>> @@ -380,15 +383,15 @@ int smp_call_function_any(const struct cpumask *mask,
>> nodemask = cpumask_of_node(cpu_to_node(cpu));
>> for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
>> cpu = cpumask_next_and(cpu, nodemask, mask)) {
>> - if (cpu_online(cpu))
>> + if (cpu_online_stable(cpu))
>> goto call;
>> }
>>
>> /* Any online will do: smp_call_function_single handles nr_cpu_ids. */
>> - cpu = cpumask_any_and(mask, cpu_online_mask);
>> + cpu = cpumask_any_and(mask, cpu_online_stable_mask);
>> call:
>> ret = smp_call_function_single(cpu, func, info, wait);
>> - put_cpu();
>> + put_online_cpus_stable_atomic();
>> return ret;
>> }
>> EXPORT_SYMBOL_GPL(smp_call_function_any);
>
> So smp_call_function_any() has no synchronization against CPUs coming
> online. Hence callers of smp_call_function_any() are responsible for
> ensuring that CPUs which are concurrently coming online will adopt the
> required state?
>
Yes.
> I guess that has always been the case...
>
Right.
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2012-12-05 12:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-04 8:53 [RFC PATCH 00/10] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2012-12-04 8:53 ` [RFC PATCH 01/10] CPU hotplug: Introduce "stable" cpu online mask, for atomic hotplug readers Srivatsa S. Bhat
2012-12-04 15:17 ` Tejun Heo
2012-12-04 21:14 ` Srivatsa S. Bhat
2012-12-04 22:10 ` Andrew Morton
2012-12-05 2:56 ` Michael Wang
2012-12-05 3:28 ` Michael Wang
2012-12-05 12:38 ` Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2012-12-04 22:17 ` Andrew Morton
2012-12-05 12:41 ` Srivatsa S. Bhat [this message]
2012-12-04 23:39 ` Rusty Russell
2012-12-05 12:44 ` Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 03/10] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 04/10] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 05/10] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 06/10] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 07/10] KVM: VMX: fix invalid cpu passed to smp_call_function_single Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 08/10] KVM: VMX: fix memory order between loading vmcs and clearing vmcs Srivatsa S. Bhat
2012-12-04 8:56 ` [RFC PATCH 09/10] KVM: VMX: fix unsyc vmcs status when cpu is going down Srivatsa S. Bhat
2012-12-04 8:56 ` [RFC PATCH 10/10] cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat
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