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 e2dbea6cee4b30c6af1054049e30903ff938f7fd..faa1c01d29170da69038e4fc80d917f42866da97 100644 (file)
--- 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;