From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: rostedt@goodmis.org, tglx@linutronix.de, peterz@infradead.org,
paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au,
mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org,
vincent.guittot@linaro.org, tj@kernel.org, sbw@mit.edu,
amit.kucheria@linaro.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 v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context
Date: Tue, 11 Dec 2012 18:34:11 +0530 [thread overview]
Message-ID: <50C72F4B.9090805@linux.vnet.ibm.com> (raw)
In-Reply-To: <20121210181521.GA30684@redhat.com>
On 12/10/2012 11:45 PM, Oleg Nesterov wrote:
> On 12/10, Srivatsa S. Bhat wrote:
>>
>> On 12/10/2012 02:27 AM, Oleg Nesterov wrote:
>>> However. If this is true, then compared to preempt_disable/stop_machine
>>> livelock is possible. Probably this is fine, we have the same problem with
>>> get_online_cpus(). But if we can accept this fact I feel we can simmplify
>>> this somehow... Can't prove, only feel ;)
>>
>> Not sure I follow..
>
> I meant that write_lock_irqsave(&hotplug_rwlock) in take_cpu_down()
> can spin "forever".
>
> Suppose that reader_acked() == T on every CPU, so that
> get_online_cpus_atomic() always takes read_lock(&hotplug_rwlock).
>
> It is possible that this lock will be never released by readers,
>
> CPU_0 CPU_1
>
> get_online_cpus_atomic()
> get_online_cpus_atomic()
> put_online_cpus_atomic()
>
> get_online_cpus_atomic()
> put_online_cpus_atomic()
>
> get_online_cpus_atomic()
> put_online_cpus_atomic()
>
> and so on.
>
Right, and we can't do anything about it :(
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2012-12-11 13:05 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-07 17:37 [RFC PATCH v3 0/9] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2012-12-07 17:38 ` [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2012-12-07 17:57 ` Tejun Heo
2012-12-07 18:16 ` Tejun Heo
2012-12-07 18:33 ` Srivatsa S. Bhat
2012-12-07 18:24 ` Srivatsa S. Bhat
2012-12-07 18:31 ` Tejun Heo
2012-12-07 18:38 ` Srivatsa S. Bhat
2012-12-09 19:14 ` Oleg Nesterov
2012-12-09 19:50 ` Srivatsa S. Bhat
2012-12-09 20:22 ` Oleg Nesterov
2012-12-10 4:28 ` Srivatsa S. Bhat
2012-12-10 17:24 ` Oleg Nesterov
2012-12-11 13:13 ` Srivatsa S. Bhat
2012-12-11 13:47 ` Tejun Heo
2012-12-11 14:02 ` Srivatsa S. Bhat
2012-12-11 14:07 ` Tejun Heo
2012-12-11 16:28 ` Srivatsa S. Bhat
2012-12-09 21:13 ` Oleg Nesterov
2012-12-10 5:01 ` Srivatsa S. Bhat
2012-12-10 17:28 ` Oleg Nesterov
2012-12-11 13:05 ` Srivatsa S. Bhat
2012-12-09 20:57 ` Oleg Nesterov
2012-12-10 5:19 ` Srivatsa S. Bhat
2012-12-10 18:15 ` Oleg Nesterov
2012-12-11 13:04 ` Srivatsa S. Bhat [this message]
2012-12-07 17:38 ` [RFC PATCH v3 2/9] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2012-12-07 17:38 ` [RFC PATCH v3 3/9] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2012-12-07 17:39 ` [RFC PATCH v3 4/9] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2012-12-07 17:39 ` [RFC PATCH v3 5/9] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() Srivatsa S. Bhat
2012-12-07 17:39 ` [RFC PATCH v3 6/9] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly Srivatsa S. Bhat
2012-12-07 17:39 ` [RFC PATCH v3 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Srivatsa S. Bhat
2012-12-09 19:48 ` Oleg Nesterov
2012-12-09 19:57 ` Srivatsa S. Bhat
2012-12-09 20:40 ` Oleg Nesterov
2012-12-10 4:04 ` Srivatsa S. Bhat
2012-12-07 17:40 ` [RFC PATCH v3 8/9] kvm, vmx: Add atomic synchronization with CPU Hotplug Srivatsa S. Bhat
2012-12-07 17:40 ` [RFC PATCH v3 9/9] cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat
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