rcu: Move rcu_report_exp_rdp() setting of ->cpu_no_qs.b.exp under lock

This commit reduces the state space of rcu_report_exp_rdp() by moving
the setting of ->cpu_no_qs.b.exp under the rcu_node structure's ->lock.
The lock isn't really all that important here, given that this per-CPU
field is supposed to be written only by its CPU, but the disabling of
interrupts excludes things like rcu_exp_handler(), which also can write
to this same field.  Avoiding this sort of interleaved access reduces
the state space.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 581e88d39542ded6d2cec67ee39b3682bfbd6576..5c4ea66cc00ddb633ee4354e9b4d1796ba082dba 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -260,8 +260,8 @@ static void rcu_report_exp_rdp(struct rcu_data *rdp)
        unsigned long flags;
        struct rcu_node *rnp = rdp->mynode;
 
-       WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
        raw_spin_lock_irqsave_rcu_node(rnp, flags);
+       WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
        rcu_report_exp_cpu_mult(rnp, flags, rdp->grpmask, true);
 }