rcu: Prevent soft-lockup complaints about no-CBs CPUs

The wait_event() at the head of the rcu_nocb_kthread() can result in
soft-lockup complaints if the CPU in question does not register RCU
callbacks for an extended period.  This commit therefore changes
the wait_event() to a wait_event_interruptible().

Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f6e5ec2..43dba2d 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2366,10 +2366,11 @@ static int rcu_nocb_kthread(void *arg)
        for (;;) {
                /* If not polling, wait for next batch of callbacks. */
                if (!rcu_nocb_poll)
-                       wait_event(rdp->nocb_wq, rdp->nocb_head);
+                       wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
                list = ACCESS_ONCE(rdp->nocb_head);
                if (!list) {
                        schedule_timeout_interruptible(1);
+                       flush_signals(current);
                        continue;
                }