From: Michael Wang <wangyun@linux.vnet.ibm.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org,
oleg@redhat.com, paulmck@linux.vnet.ibm.com,
rusty@rustcorp.com.au, mingo@kernel.org,
akpm@linux-foundation.org, namhyung@kernel.org,
walken@google.com, vincent.guittot@linaro.org,
laijs@cn.fujitsu.com, David.Laight@aculab.com,
rostedt@goodmis.org, xiaoguangrong@linux.vnet.ibm.com,
sbw@mit.edu, fweisbec@gmail.com, zhong@linux.vnet.ibm.com,
nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org,
linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Wang YanQing <udknight@gmail.com>, Shaohua Li <shli@fusionio.com>,
Jan Beulich <jbeulich@suse.com>,
liguang <lig.fnst@cn.fujitsu.com>
Subject: Re: [PATCH v3 10/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline
Date: Tue, 02 Jul 2013 16:47:24 +0800 [thread overview]
Message-ID: <51D2939C.5090205@linux.vnet.ibm.com> (raw)
In-Reply-To: <51D28E69.9060205@linux.vnet.ibm.com>
On 07/02/2013 04:25 PM, Srivatsa S. Bhat wrote:
> Hi Michael,
>
> On 07/02/2013 11:02 AM, Michael Wang wrote:
>> Hi, Srivatsa
>>
>> On 06/28/2013 03:54 AM, Srivatsa S. Bhat wrote:
>> [snip]
>>> @@ -625,8 +632,9 @@ EXPORT_SYMBOL(on_each_cpu_mask);
>>> * The function might sleep if the GFP flags indicates a non
>>> * atomic allocation is allowed.
>>> *
>>> - * Preemption is disabled to protect against CPUs going offline but not online.
>>> - * CPUs going online during the call will not be seen or sent an IPI.
>>> + * We use get/put_online_cpus_atomic() to protect against CPUs going
>>> + * offline but not online. CPUs going online during the call will
>>> + * not be seen or sent an IPI.
>>
>> I was a little confused about this comment, if the offline-cpu still
>> have chances to become online, then there is chances that we will pick
>> it from for_each_online_cpu(), isn't it? Did I miss some point?
>>
>
> Whether or not the newly onlined CPU is observed in our for_each_online_cpu()
> loop, is dependent on timing. On top of that, there are 2 paths in the code:
> one which uses a temporary cpumask and the other which doesn't. In the former
> case, if a CPU comes online _after_ we populate the temporary cpumask, then
> we won't send an IPI to that cpu, since the temporary cpumask doesn't contain
> that CPU. Whereas, if we observe the newly onlined CPU in the for_each_online_cpu()
> loop itself (either in the former or the latter case), then yes, we will send
> the IPI to that CPU.
So it is not 'during the call' but 'during the call of
on_each_cpu_mask()', correct?
The comment position seems like it declaim that during the call of this
func, online-cpu won't be seem and send IPI...
Regards,
Michael Wang
>
> Regards,
> Srivatsa S. Bhat
>
>>
>>> *
>>> * You must not call this function with disabled interrupts or
>>> * from a hardware interrupt handler or from a bottom half handler.
>>> @@ -641,26 +649,26 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
>>> might_sleep_if(gfp_flags & __GFP_WAIT);
>>>
>>> if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
>>> - preempt_disable();
>>> + get_online_cpus_atomic();
>>> for_each_online_cpu(cpu)
>>> if (cond_func(cpu, info))
>>> cpumask_set_cpu(cpu, cpus);
>>> on_each_cpu_mask(cpus, func, info, wait);
>>> - preempt_enable();
>>> + put_online_cpus_atomic();
>>> free_cpumask_var(cpus);
>>> } else {
>>> /*
>>> * No free cpumask, bother. No matter, we'll
>>> * just have to IPI them one by one.
>>> */
>>> - preempt_disable();
>>> + get_online_cpus_atomic();
>>> for_each_online_cpu(cpu)
>>> if (cond_func(cpu, info)) {
>>> ret = smp_call_function_single(cpu, func,
>>> info, wait);
>>> WARN_ON_ONCE(!ret);
>>> }
>>> - preempt_enable();
>>> + put_online_cpus_atomic();
>>> }
>>> }
>>> EXPORT_SYMBOL(on_each_cpu_cond);
>>>
>>
>
> --
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next prev parent reply other threads:[~2013-07-02 8:47 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-27 19:52 [PATCH v3 00/45] CPU hotplug: stop_machine()-free CPU hotplug, part 1 Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 01/45] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 02/45] CPU hotplug: Clarify the usage of different synchronization APIs Srivatsa S. Bhat
2013-06-27 19:52 ` [PATCH v3 03/45] Documentation, CPU hotplug: Recommend usage of get/put_online_cpus_atomic() Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 04/45] CPU hotplug: Add infrastructure to check lacking hotplug synchronization Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 05/45] CPU hotplug: Protect set_cpu_online() to avoid false-positives Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 06/45] CPU hotplug: Sprinkle debugging checks to catch locking bugs Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 07/45] CPU hotplug: Add _nocheck() variants of accessor functions Srivatsa S. Bhat
2013-06-27 19:53 ` [PATCH v3 08/45] CPU hotplug: Expose the new debug config option Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 09/45] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 10/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-07-02 5:32 ` Michael Wang
2013-07-02 8:25 ` Srivatsa S. Bhat
2013-07-02 8:47 ` Michael Wang [this message]
2013-07-02 9:51 ` Srivatsa S. Bhat
2013-07-02 10:08 ` Michael Wang
2013-06-27 19:54 ` [PATCH v3 11/45] sched/core: " Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 12/45] migration: Use raw_spin_lock/unlock since interrupts are already disabled Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 13/45] sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 14/45] timer: " Srivatsa S. Bhat
2013-06-27 19:54 ` [PATCH v3 15/45] sched/rt: " Srivatsa S. Bhat
2013-06-27 19:55 ` [PATCH v3 16/45] rcu: Use cpu_is_offline_nocheck() to avoid false-positive warnings Srivatsa S. Bhat
2013-06-27 20:12 ` Paul E. McKenney
2013-06-27 19:55 ` [PATCH v3 17/45] tick-broadcast: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:55 ` [PATCH v3 18/45] time/clocksource: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 19/45] softirq: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 20/45] irq: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 21/45] net: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 22/45] block: " Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 23/45] percpu_counter: Use _nocheck version of for_each_online_cpu() Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 24/45] infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 19:56 ` [PATCH v3 25/45] [SCSI] fcoe: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 26/45] staging/octeon: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 27/45] x86: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 28/45] perf/x86: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 29/45] KVM: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 30/45] x86/xen: " Srivatsa S. Bhat
2013-06-27 19:57 ` [PATCH v3 31/45] alpha/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 32/45] blackfin/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 33/45] cris/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 34/45] hexagon/smp: " Srivatsa S. Bhat
2013-06-27 19:58 ` [PATCH v3 35/45] ia64: irq, perfmon: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 36/45] ia64: smp, tlb: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 37/45] m32r: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 38/45] MIPS: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 39/45] mn10300: " Srivatsa S. Bhat
2013-06-27 19:59 ` [PATCH v3 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 41/45] powerpc: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 43/45] sh: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 44/45] sparc: " Srivatsa S. Bhat
2013-06-27 20:00 ` [PATCH v3 45/45] tile: " Srivatsa S. Bhat
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