[PATCH 3/3] rcu: Assume rcu_report_dead() always deals with local CPU

From: Frederic Weisbecker
Date: Tue May 18 2021 - 20:09:48 EST

rcu_report_dead() is always called locally from the idle path. Passing
a CPU number to it suggests otherwise and is rather error-prone as the
code inside relies on locality.

Robustify the function prototype and refine the name along the way.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
.../Expedited-Grace-Periods/Expedited-Grace-Periods.rst | 2 +-
Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg | 2 +-
Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg | 2 +-
.../RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg | 2 +-
Documentation/RCU/Design/Requirements/Requirements.rst | 2 +-
arch/arm64/kernel/smp.c | 2 +-
include/linux/rcupdate.h | 2 +-
kernel/cpu.c | 4 ++--
kernel/rcu/tree.c | 6 +++---
9 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
index 6f89cf1e567d..eddf5eea94f1 100644
--- a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
+++ b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
@@ -181,7 +181,7 @@ operations is carried out at several levels:
of this wait (or series of waits, as the case may be) is to permit a
concurrent CPU-hotplug operation to complete.
#. In the case of RCU-sched, one of the last acts of an outgoing CPU is
- to invoke ``rcu_report_dead()``, which reports a quiescent state for
+ to invoke ``rcu_report_dead_cpu()``, which reports a quiescent state for
that CPU. However, this is likely paranoia-induced redundancy.

+-----------------------------------------------------------------------+
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
index 7ddc094d7f28..6e7b05ff00d3 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
@@ -1135,7 +1135,7 @@
font-weight="bold"
font-size="192"
id="text202-7-5-3-27-6-5"
- style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
+ style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead_cpu()</text>
<text
xml:space="preserve"
x="3745.7725"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
index 069f6f8371c2..ede6ae66d286 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
@@ -3274,7 +3274,7 @@
font-weight="bold"
font-size="192"
id="text202-7-5-3-27-6-5"
- style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
+ style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead_cpu()</text>
<text
xml:space="preserve"
x="3745.7725"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
index 2c9310ba29ba..e0ab8cd8db2d 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
@@ -607,7 +607,7 @@
font-weight="bold"
font-size="192"
id="text202-7-5-3-27-6"
- style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
+ style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead_cpu()</text>
<text
xml:space="preserve"
x="3745.7725"
diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 38a39476fc24..ede6a2bbf69d 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1953,7 +1953,7 @@ if offline CPUs block an RCU grace period for too long.

An offline CPU's quiescent state will be reported either:

-1. As the CPU goes offline using RCU's hotplug notifier (rcu_report_dead()).
+1. As the CPU goes offline using RCU's hotplug notifier (rcu_report_dead_cpu()).
2. When grace period initialization (rcu_gp_init()) detects a
race either with CPU offlining or with a task unblocking on a leaf
``rcu_node`` structure whose CPUs are all offline.
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index dcd7041b2b07..74c0ae3d6c93 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -414,7 +414,7 @@ void cpu_die_early(void)

/* Mark this CPU absent */
set_cpu_present(cpu, 0);
- rcu_report_dead(cpu);
+ rcu_report_dead_cpu();

if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
update_cpu_boot_status(CPU_KILL_ME);
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d9680b798b21..fda1dc9b4e03 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -85,7 +85,7 @@ static inline int rcu_preempt_depth(void)
void rcu_init(void);
extern int rcu_scheduler_active __read_mostly;
void rcu_sched_clock_irq(int user);
-void rcu_report_dead(unsigned int cpu);
+void rcu_report_dead_cpu(void);
void rcutree_migrate_callbacks(int cpu);

#ifdef CONFIG_TASKS_RCU_GENERIC
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e538518556f4..852fcbda1fd8 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1016,10 +1016,10 @@ void cpuhp_report_idle_dead(void)
struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

BUG_ON(st->state != CPUHP_AP_OFFLINE);
- rcu_report_dead(smp_processor_id());
+ rcu_report_dead_cpu();
st->state = CPUHP_AP_IDLE_DEAD;
/*
- * We cannot call complete after rcu_report_dead() so we delegate it
+ * We cannot call complete after rcu_report_dead_cpu() so we delegate it
* to an online cpu.
*/
smp_call_function_single(cpumask_first(cpu_online_mask),
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a6b448e6e059..824a3b367797 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4322,11 +4322,11 @@ void rcu_cpu_starting(unsigned int cpu)
* from the outgoing CPU rather than from the cpuhp_step mechanism.
* This is because this function must be invoked at a precise location.
*/
-void rcu_report_dead(unsigned int cpu)
+void rcu_report_dead_cpu(void)
{
unsigned long flags;
unsigned long mask;
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */

// Do any dangling deferred wakeups.
@@ -4334,7 +4334,7 @@ void rcu_report_dead(unsigned int cpu)

/* QS for any half-done expedited grace period. */
preempt_disable();
- rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
+ rcu_report_exp_rdp(rdp);
preempt_enable();
rcu_preempt_deferred_qs(current);

--
2.25.1