linux-kernel - [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaints about no-CBs CPUs

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Message-Id: <1357405131-13421-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Sat,  5 Jan 2013 08:58:50 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/urgent 1/2] rcu: Prevent soft-lockup complaints about no-CBs CPUs

From: Paul Gortmaker <paul.gortmaker@...driver.com>

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@...il.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f6e5ec2..43dba2d 100644
--- 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;
 		}
 
-- 
1.7.8

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