[PATCH] rcu: Improve detection of illegal synchronize_rcu() call from RCU read side

[Frederic Weisbecker]

In RCU tree, synchronize_{rcu,sched,rcu_bh} can detect illegal call from
RCU read side critical section with might_sleep() called before waiting
for the grace period completion.

But in RCU tree, the calls to synchronize_sched() and synchronize_rcu_bh()
return immediately if only one CPU is running. In this case we are missing
the checks for calls of these APIs from atomic sections (including RCU read
side).

To cover every cases, put a might_sleep() call in the beginning of those
two functions.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
 kernel/rcutree.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6c4a672..68cded7 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1816,6 +1816,12 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
  */
 void synchronize_sched(void)
 {
+	/*
+	 * Detect we are not calling this while in RCU
+	 * read side critical section, even with 1 online
+	 * CPU.
+	 */
+	might_sleep();
 	if (rcu_blocking_is_gp())
 		return;
 	wait_rcu_gp(call_rcu_sched);
@@ -1833,6 +1839,12 @@ EXPORT_SYMBOL_GPL(synchronize_sched);
  */
 void synchronize_rcu_bh(void)
 {
+	/*
+	 * Detect we are not calling this while in RCU
+	 * read side critical section, even with 1 online
+	 * CPU.
+	 */
+	might_sleep();
 	if (rcu_blocking_is_gp())
 		return;
 	wait_rcu_gp(call_rcu_bh);
-- 
1.7.0.4
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