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    SubjectRe: [PATCH 8/9] jrcu: fix broken rcu_barrier
    On Mon, Mar 14, 2011 at 06:09:28PM -0400, Joe Korty wrote:
    > On Mon, Mar 14, 2011 at 04:47:18AM -0400, Paul E. McKenney wrote:
    > > On Sun, Mar 13, 2011 at 11:50:44PM -0400, Joe Korty wrote:
    > > > +void rcu_barrier(void)
    > > > +{
    > > > + synchronize_sched();
    > > > + synchronize_sched();
    > > > +}
    > >
    > > This is still broken. You need to wait until all pre-existing RCU
    > > callbacks on all CPUs have been invoked. Although this does guarantee
    > > that all callbacks on the current CPU have been invoked, if one of the
    > > other CPUs is busy, it might not yet have processed the callbacks from
    > > earlier grace periods. The usual way to take care of this is to post
    > > a callback on each CPU, then wait for them all to be invoked.
    >
    > Hi Paul,
    > JRCU (eventually) chains together all callbacks from all
    > cpus into a single queue and then it expires that single
    > queue. So the double synchronize_sched() should work as
    > a rcu_barrier implementation.

    Hello, Joe,

    So the following grace period is not permitted to start until all of
    the callbacks from the prior grace period have been invoked?

    Or am I missing something subtle here?

    Thanx, Paul


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