rcu: Make rcu_barrier() less disruptive

The rcu_barrier() primitive interrupts each and every CPU, registering
a callback on every CPU.  Once all of these callbacks have been invoked,
rcu_barrier() knows that every callback that was registered before
the call to rcu_barrier() has also been invoked.

However, there is no point in registering a callback on a CPU that
currently has no callbacks, most especially if that CPU is in a
deep idle state.  This commit therefore makes rcu_barrier() avoid
interrupting CPUs that have no callbacks.  Doing this requires reworking
the handling of orphaned callbacks, otherwise callbacks could slip through
rcu_barrier()'s net by being orphaned from a CPU that rcu_barrier() had
not yet interrupted to a CPU that rcu_barrier() had already interrupted.
This reworking was needed anyway to take a first step towards weaning
RCU from the CPU_DYING notifier's use of stop_cpu().

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index ed459edeff43..d4bc16ddd1d4 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -271,13 +271,13 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 
         gpnum = rsp->gpnum;
         seq_printf(m, "c=%lu g=%lu s=%d jfq=%ld j=%x "
-                      "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu\n",
+                      "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
                    rsp->completed, gpnum, rsp->fqs_state,
                    (long)(rsp->jiffies_force_qs - jiffies),
                    (int)(jiffies & 0xffff),
                    rsp->n_force_qs, rsp->n_force_qs_ngp,
                    rsp->n_force_qs - rsp->n_force_qs_ngp,
-                   rsp->n_force_qs_lh);
+                   rsp->n_force_qs_lh, rsp->qlen_lazy, rsp->qlen);
         for (rnp = &rsp->node[0]; rnp - &rsp->node[0] < NUM_RCU_NODES; rnp++) {
                 if (rnp->level != level) {
                         seq_puts(m, "\n");