Messages in this thread | | | Date | Wed, 12 Dec 2012 18:24:31 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC PATCH v4 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context |
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On 12/12, Oleg Nesterov wrote: > > On 12/11, Srivatsa S. Bhat wrote: > > > > IOW, the hotplug readers just increment/decrement their per-cpu refcounts > > when no writer is active. > > plus cli/sti ;) and increment/decrement are atomic. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
OOPS, sorry I was going to say "adds mb()".
And when I look at get_online_cpus_atomic() again it uses rmb(). This doesn't look correct, we need the full barrier between this_cpu_inc() and writer_active().
At the same time reader_nested_percpu() can be checked before mb().
Oleg.
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