From: Paul E. McKenney <paulmck@kernel.org>
Date: Fri, 7 Apr 2023 23:47:34 +0000 (-0700)
Subject: rcu: Mark rcu_cpu_kthread() accesses to ->rcu_cpu_has_work
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a24c1aab652ebacf9ea62470a166514174c96fe1;p=linux.git

rcu: Mark rcu_cpu_kthread() accesses to ->rcu_cpu_has_work

The rcu_data structure's ->rcu_cpu_has_work field can be modified by
any CPU attempting to wake up the rcuc kthread.  Therefore, this commit
marks accesses to this field from the rcu_cpu_kthread() function.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e2dbea6cee4b3..faa1c01d29170 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2481,12 +2481,12 @@ static void rcu_cpu_kthread(unsigned int cpu)
 		*statusp = RCU_KTHREAD_RUNNING;
 		local_irq_disable();
 		work = *workp;
-		*workp = 0;
+		WRITE_ONCE(*workp, 0);
 		local_irq_enable();
 		if (work)
 			rcu_core();
 		local_bh_enable();
-		if (*workp == 0) {
+		if (!READ_ONCE(*workp)) {
 			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
 			*statusp = RCU_KTHREAD_WAITING;
 			return;