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Date: Thu, 13 Feb 2014 18:44:52 +0100 From: Oleg Nesterov <oleg@...hat.com> To: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> Cc: Toshi Kani <toshi.kani@...com>, paulus@...ba.org, rusty@...tcorp.com.au, peterz@...radead.org, tglx@...utronix.de, akpm@...ux-foundation.org, mingo@...nel.org, paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com, ego@...ux.vnet.ibm.com, linux@....linux.org.uk, linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com> Subject: Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback registration functions On 02/12, Srivatsa S. Bhat wrote: > > On 02/11/2014 10:45 PM, Oleg Nesterov wrote: > > > > I am a bit confused... If we do this, why we can't simply turn > > cpu_add_remove_lock into rw_semaphore? [...snip...] > cpu_notifier_register_begin(); | Run in parallel > | with similar phases > for_each_online_cpu(cpu) | from other subsystems. > init_cpu(cpu); | > > /* Updates the cpu notifier chain. */ > register_cpu_notifier(&foobar_cpu_notifier); ||| -- Must run serially Ah indeed, we can't use a single lock, thanks. Perhaps we can simply add a spinlock_t which only protects cpu_chain though, but I am not sure and currently this is off-topic anyway. Thanks, Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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