rcu: Mark __rcu_irq_enter_check_tick() ->rcu_urgent_qs load

The rcu_request_urgent_qs_task() function does a cross-CPU store
to ->rcu_urgent_qs, so this commit therefore marks the load in
__rcu_irq_enter_check_tick() with READ_ONCE().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f788981..cb1caef 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -632,7 +632,7 @@ void __rcu_irq_enter_check_tick(void)
        // prevents self-deadlock.  So we can safely recheck under the lock.
        // Note that the nohz_full state currently cannot change.
        raw_spin_lock_rcu_node(rdp->mynode);
-       if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
+       if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
                // A nohz_full CPU is in the kernel and RCU needs a
                // quiescent state.  Turn on the tick!
                WRITE_ONCE(rdp->rcu_forced_tick, true);