Messages in this thread | | | Date | Sun, 10 Feb 2013 21:13:12 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH v5 04/45] percpu_rwlock: Implement the core design of Per-CPU Reader-Writer Locks |
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On 02/11, Srivatsa S. Bhat wrote: > > On 02/09/2013 04:40 AM, Paul E. McKenney wrote: > >> +static void announce_writer_inactive(struct percpu_rwlock *pcpu_rwlock) > >> +{ > >> + unsigned int cpu; > >> + > >> + drop_writer_signal(pcpu_rwlock, smp_processor_id()); > > > > Why do we drop ourselves twice? More to the point, why is it important to > > drop ourselves first? > > > > I don't see where we are dropping ourselves twice. Note that we are no longer > in the cpu_online_mask, so the 'for' loop below won't include us. So we need > to manually drop ourselves. It doesn't matter whether we drop ourselves first > or later.
Yes, but this just reflects its usage in cpu-hotplug. cpu goes away under _write_lock.
Perhaps _write_lock/unlock shoud use for_each_possible_cpu() instead?
Hmm... I think this makes sense anyway. Otherwise, in theory, percpu_write_lock(random_non_hotplug_lock) can race with cpu_up?
Oleg.
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