linux-kernel - [PATCH tip/core/rcu 02/47] rcu: Improve synchronize

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Date:	Fri,  3 Feb 2012 17:44:37 -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, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 02/47] rcu: Improve synchronize_rcu() diagnostics

From: Frederic Weisbecker <fweisbec@...il.com>

Although TREE_PREEMPT_RCU indirectly uses might_sleep() to detect illegal
use of synchronize_sched() and synchronize_rcu_bh() from within an RCU
read-side critical section, this might_sleep() check is bypassed when
there is only a single CPU (for example, when running an SMP kernel on
a single-CPU system).  This patch therefore adds a might_sleep() call
to the rcu_blocking_is_gp() check that is unconditionally invoked from
both synchronize_sched() and synchronize_rcu_bh().

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/rcutree.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 6745846..73e7195 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -83,6 +83,7 @@ extern void rcu_sched_force_quiescent_state(void);
 /* A context switch is a grace period for RCU-sched and RCU-bh. */
 static inline int rcu_blocking_is_gp(void)
 {
+	might_sleep();  /* Check for RCU read-side critical section. */
 	return num_online_cpus() == 1;
 }
 
-- 
1.7.8

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