rcu: RCU_FAST_NO_HZ detection of callback adoption

In the present implementations of CPU hotplug, the outgoing CPU is
guaranteed to run its stop-machine process on the way out, which
will guarantee that RCU_FAST_NO_HZ forces the CPU out of dyntick-idle
mode.

However, new versions of CPU hotplug might not work this way.  This
commit therefore removes this design constraint by explicitly notifying
CPUs when they adopt non-lazy RCU callbacks.

Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Tested-by: Heiko Carstens <[email protected]>
Tested-by: Pascal Chapperon <[email protected]>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0da7b88d92d0a599242e8dcf70ab566d3e23b687..3b0f1337f75b93e9c320a97fa7117c7c09e5599b 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1397,6 +1397,8 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
        rdp->qlen_lazy += rsp->qlen_lazy;
        rdp->qlen += rsp->qlen;
        rdp->n_cbs_adopted += rsp->qlen;
+       if (rsp->qlen_lazy != rsp->qlen)
+               rcu_idle_count_callbacks_posted();
        rsp->qlen_lazy = 0;
        rsp->qlen = 0;