Re: [RFC PATCH v3 1/9] CPU hotplug: Provide APIs to prevent CPUoffline from atomic context

[Oleg Nesterov]

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.

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