rcu: update documentation/comments for Lai's adoption patch
Lai's RCU-callback immediate-adoption patch changes the RCU tracing
output, so update tracing.txt. Also update a few comments to clarify
the synchronization design.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 669d7fe..120820f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1668,7 +1668,9 @@
* decrement rcu_barrier_cpu_count -- otherwise the first CPU
* might complete its grace period before all of the other CPUs
* did their increment, causing this function to return too
- * early.
+ * early. Note that on_each_cpu() disables irqs, which prevents
+ * any CPUs from coming online or going offline until each online
+ * CPU has queued its RCU-barrier callback.
*/
atomic_set(&rcu_barrier_cpu_count, 1);
on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
@@ -1797,9 +1799,9 @@
case CPU_DYING:
case CPU_DYING_FROZEN:
/*
- * The whole machine is "stopped" except this cpu, so we can
- * touch any data without introducing corruption. And we send
- * the callbacks to an attribute chosen online cpu.
+ * The whole machine is "stopped" except this CPU, so we can
+ * touch any data without introducing corruption. We send the
+ * dying CPU's callbacks to an arbitrarily chosen online CPU.
*/
rcu_send_cbs_to_online(&rcu_bh_state);
rcu_send_cbs_to_online(&rcu_sched_state);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 0de359b..643c8f6 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -774,7 +774,7 @@
}
/*
- * Move preemptable DYING RCU's callbacks to other online CPU.
+ * Move preemptable RCU's callbacks from dying CPU to other online CPU.
*/
static void rcu_preempt_send_cbs_to_online(void)
{