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    SubjectRe: [RFC PATCH v2] Add rcu user eqs exception hooks for async page fault
    From
    2012/11/28 Gleb Natapov <gleb@redhat.com>:
    > On Wed, Nov 28, 2012 at 01:55:42PM +0100, Frederic Weisbecker wrote:
    >> Yes but if rcu_irq_*() calls are fine to be called there, and I
    >> believe they are because exception_enter() exits the user mode, we
    >> should start to protect there right now instead of waiting for a
    >> potential future warning of illegal RCU use.
    >>
    > Async page not present is not much different from regular page fault
    > exception when it happens not on idle task (regular #PF cannot happen
    > on idle task), but code have a special handling for idle task. So why
    > do you think rcu_irq_*() is required here, but not in page fault
    > handler?

    Because we are not supposed to fault in idle, at least I hope there
    are no case around. Except on cases like here with KVM I guess but we
    have that special async handler for that.

    Note exception_enter() only takes cares of RCU user mode, not idle. If
    the need arise in the future we can extend it to handle idle.

    >> >
    >> > I think we still need Gleb's patch about the idle check in
    >> > kvm_async_pf_task_wait(), and maybe another patch for the
    >> > exit_idle()/enter_idle() issue.
    >>
    >> Right.
    >>
    > Done.

    Thanks!


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