[PATCH RFC tip/core/rcu 02/41] rcu: Improve synchronize_rcu() diagnostics

From: Paul E. McKenney
Date: Wed Feb 01 2012 - 14:49:58 EST

From: Frederic Weisbecker <fweisbec@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
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;


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