linux-kernel - [PATCH rcu 5/5] rcu: Create and use an rcu_rdp_cpu

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Date:   Fri,  4 Feb 2022 15:20:36 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 5/5] rcu: Create and use an rcu_rdp_cpu_online()

The pattern "rdp->grpmask & rcu_rnp_online_cpus(rnp)" occurs frequently
in RCU code in order to determine whether rdp->cpu is online from an
RCU perspective.  This commit therefore creates an rcu_rdp_cpu_online()
function to replace it.

[ paulmck: Apply kernel test robot unused-variable feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c        | 21 +++++++++++++--------
 kernel/rcu/tree_plugin.h |  6 ++----
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1c30a01692076..6a470bb93b485 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -222,6 +222,16 @@ static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
 	return READ_ONCE(rnp->qsmaskinitnext);
 }
 
+/*
+ * Is the CPU corresponding to the specified rcu_data structure online
+ * from RCU's perspective?  This perspective is given by that structure's
+ * ->qsmaskinitnext field rather than by the global cpu_online_mask.
+ */
+static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
+{
+	return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
+}
+
 /*
  * Return true if an RCU grace period is in progress.  The READ_ONCE()s
  * permit this function to be invoked without holding the root rcu_node
@@ -1168,14 +1178,12 @@ void rcu_request_urgent_qs_task(struct task_struct *t)
 bool rcu_lockdep_current_cpu_online(void)
 {
 	struct rcu_data *rdp;
-	struct rcu_node *rnp;
 	bool ret = false;
 
 	if (in_nmi() || !rcu_scheduler_fully_active)
 		return true;
 	preempt_disable_notrace();
 	rdp = this_cpu_ptr(&rcu_data);
-	rnp = rdp->mynode;
 	/*
 	 * Strictly, we care here about the case where the current CPU is
 	 * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
@@ -1183,8 +1191,7 @@ bool rcu_lockdep_current_cpu_online(void)
 	 * false positive if it's held by some *other* CPU, but that's
 	 * OK because that just means a false *negative* on the warning.
 	 */
-	if (rdp->grpmask & rcu_rnp_online_cpus(rnp) ||
-	    arch_spin_is_locked(&rcu_state.ofl_lock))
+	if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
 		ret = true;
 	preempt_enable_notrace();
 	return ret;
@@ -1269,8 +1276,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	 * For more detail, please refer to the "Hotplug CPU" section
 	 * of RCU's Requirements documentation.
 	 */
-	if (WARN_ON_ONCE(!(rdp->grpmask & rcu_rnp_online_cpus(rnp)))) {
-		bool onl;
+	if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
 		struct rcu_node *rnp1;
 
 		pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
@@ -1279,9 +1285,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 		for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
 			pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
 				__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
-		onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
 		pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
-			__func__, rdp->cpu, ".o"[onl],
+			__func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
 			(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
 			(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
 		return 1; /* Break things loose after complaining. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c5b45c2f68a15..d3db2168598ef 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -330,7 +330,7 @@ void rcu_note_context_switch(bool preempt)
 		 * then queue the task as required based on the states
 		 * of any ongoing and expedited grace periods.
 		 */
-		WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
+		WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp));
 		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
 		trace_rcu_preempt_task(rcu_state.name,
 				       t->pid,
@@ -773,7 +773,6 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 	int cpu;
 	int i;
 	struct list_head *lhp;
-	bool onl;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp1;
 
@@ -797,9 +796,8 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 	pr_cont("\n");
 	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
 		rdp = per_cpu_ptr(&rcu_data, cpu);
-		onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
 		pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
-			cpu, ".o"[onl],
+			cpu, ".o"[rcu_rdp_cpu_online(rdp)],
 			(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
 			(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
 	}
-- 
2.31.1.189.g2e36527f23