[tip: core/rcu] rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_kick_kthreads

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     fe63b723cc7ca3a91ea91274e0f2cba29452b3fa
Gitweb:        https://git.kernel.org/tip/fe63b723cc7ca3a91ea91274e0f2cba29452b3fa
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Tue, 23 Jun 2020 18:04:45 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 24 Aug 2020 18:36:07 -07:00

rcu: Add READ_ONCE() to rcu_do_batch() access to rcu_kick_kthreads

Given that sysfs can change the value of rcu_kick_kthreads at any time,
this commit adds a READ_ONCE() to the sole access to that variable.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree_stall.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index b5d3b47..a1780a6 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -158,7 +158,7 @@ static void rcu_stall_kick_kthreads(void)
 {
 	unsigned long j;
 
-	if (!rcu_kick_kthreads)
+	if (!READ_ONCE(rcu_kick_kthreads))
 		return;
 	j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
 	if (time_after(jiffies, j) && rcu_state.gp_kthread &&
@@ -580,7 +580,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 	unsigned long js;
 	struct rcu_node *rnp;
 
-	if ((rcu_stall_is_suppressed() && !rcu_kick_kthreads) ||
+	if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
 	    !rcu_gp_in_progress())
 		return;
 	rcu_stall_kick_kthreads();