Commit a4382659 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney
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rcu: Ignore rdp.cpu_no_qs.b.exp on preemptible RCU's rcu_qs() 



Preemptible RCU does not use the rcu_data structure's ->cpu_no_qs.b.exp,
instead using a separate ->exp_deferred_qs field to record the need for
an expedited quiescent state.

In fact ->cpu_no_qs.b.exp should never be set in preemptible RCU because
preemptible RCU's expedited grace periods use other mechanisms to record
quiescent states.

This commit therefore removes the implicit rcu_qs() reference to
->cpu_no_qs.b.exp in favor of a direct reference to ->cpu_no_qs.b.norm.

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 8c0abfd6

kernel/rcu/tree_plugin.h

+5 −1
Original line number Diff line number Diff line
@@ -277,12 +277,16 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 
 * current task, there might be any number of other tasks blocked while

 * in an RCU read-side critical section.

 *

 * Unlike non-preemptible-RCU, quiescent state reports for expedited

 * grace periods are handled separately via deferred quiescent states

 * and context switch events.

 *

 * Callers to this function must disable preemption.

 */

static void rcu_qs(void)

{

	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");

	if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {

	if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {

		trace_rcu_grace_period(TPS("rcu_preempt"),

				       __this_cpu_read(rcu_data.gp_seq),

				       TPS("cpuqs"));