[RFC] rcu: Prevent expedite reporting within RCU read-side section

[Byungchul Park]

We report the quiescent state for this cpu if it's out of RCU read-side
section at the moment IPI was just fired during the expedite process.

However, current code reports the quiescent state even in the case:

   1) the current task is still within a RCU read-side section
   2) the current task has been blocked within the RCU read-side section

Since we don't get to the quiescent state yet in the case, we shouldn't
report it but check it another time.

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
 kernel/rcu/tree_exp.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 73e1d3d..cc69d14 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -731,13 +731,13 @@ static void sync_rcu_exp_handler(void *info)
 	/*
 	 * We are either exiting an RCU read-side critical section (negative
 	 * values of t->rcu_read_lock_nesting) or are not in one at all
-	 * (zero value of t->rcu_read_lock_nesting).  Or we are in an RCU
-	 * read-side critical section that blocked before this expedited
-	 * grace period started.  Either way, we can immediately report
-	 * the quiescent state.
+	 * (zero value of t->rcu_read_lock_nesting). We can immediately
+	 * report the quiescent state.
 	 */
-	rdp = this_cpu_ptr(rsp->rda);
-	rcu_report_exp_rdp(rsp, rdp, true);
+	if (t->rcu_read_lock_nesting <= 0) {
+		rdp = this_cpu_ptr(rsp->rda);
+		rcu_report_exp_rdp(rsp, rdp, true);
+	}
 }
 
 /**
-- 
1.9.1