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    SubjectRe: Real-Time Preemption and RCU
    On Fri, Mar 18, 2005 at 04:56:41AM -0800, Bill Huey wrote:
    > On Thu, Mar 17, 2005 at 04:20:26PM -0800, Paul E. McKenney wrote:
    > > 5. Scalability -and- Realtime Response.
    > ...
    >
    > > void
    > > rcu_read_lock(void)
    > > {
    > > preempt_disable();
    > > if (current->rcu_read_lock_nesting++ == 0) {
    > > current->rcu_read_lock_ptr =
    > > &__get_cpu_var(rcu_data).lock;
    > > read_lock(current->rcu_read_lock_ptr);
    > > }
    > > preempt_enable();
    > > }
    >
    > Ok, here's a rather unsure question...
    >
    > Uh, is that a sleep violation if that is exclusively held since it
    > can block within an atomic critical section (deadlock) ?

    Hey, I wasn't joking when I said that I probably got something wrong! ;-)

    My current thought is that the preempt_disable()/preempt_enable() can
    be dropped entirely. Messes up any tool that browses through
    ->rcu_read_lock_nesting, but don't see any other problem. Yet, anyway!

    Thanx, Paul
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