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From: Oleg Nesterov <oleg@redhat.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
	rostedt@goodmis.org
Cc: 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: Sun, 9 Dec 2012 21:57:33 +0100	[thread overview]
Message-ID: <20121209205733.GA7038@redhat.com> (raw)
In-Reply-To: <20121207173759.27305.84316.stgit@srivatsabhat.in.ibm.com>

On 12/07, Srivatsa S. Bhat wrote:
>
> 4. No deadlock possibilities
>
>    Per-cpu locking is not the way to go if we want to have relaxed rules
>    for lock-ordering. Because, we can end up in circular-locking dependencies
>    as explained in https://lkml.org/lkml/2012/12/6/290

OK, but this assumes that, contrary to what Steven said, read-write-read
deadlock is not possible when it comes to rwlock_t. So far I think this
is true and we can't deadlock. Steven?

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 ;)

Oleg.


  parent reply	other threads:[~2012-12-09 20:57 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 [this message]
2012-12-10  5:19     ` Srivatsa S. Bhat
2012-12-10 18:15       ` Oleg Nesterov
2012-12-11 13:04         ` Srivatsa S. Bhat
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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