Subject: [PATCH] perf: Fix topology_sibling_cpumask check warning on ARM

From: [email-masked]
Date: Thu, 12 Sep 2024 07:50:25 -0700

From: Kan Liang <[email-masked]>

The below warning is triggered when building with arm
multi_v7_defconfig.

kernel/events/core.c: In function 'perf_event_setup_cpumask':
kernel/events/core.c:14012:13: warning: the comparison will always
evaluate as 'true' for the address of 'thread_sibling' will never be
NULL [-Waddress]
14012 |         if (!topology_sibling_cpumask(cpu)) {

The perf_event_init_cpu() may be invoked at the early boot stage, while
the topology_*_cpumask hasn't been initialized yet. The check is to
specially handle the case, and initialize the perf_online_<domain>_masks
on the boot CPU.
X86 uses a per-cpu cpumask pointer, which could be NULL at the early
boot stage. However, ARM uses a global variable, which never be NULL.

Use perf_online_mask as an indicator instead. Only initialize the
perf_online_<domain>_masks when perf_online_mask is empty.

Fix a typo as well.

Fixes: 4ba4f1afb6a9 ("perf: Generic hotplug support for a PMU with a scope")
Reported-by: Stephen Rothwell <[email-masked]>
Closes: https://lore.kernel.org/lkml/[email-masked]/
Reported-by: Steven Price <[email-masked]>
Closes: https://lore.kernel.org/lkml/[email-masked]/
Signed-off-by: Kan Liang <[email-masked]>
---
 kernel/events/core.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7a028474caef..20e97c1aa4d6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13954,21 +13954,19 @@ static void perf_event_setup_cpumask(unsigned int cpu)
 	struct cpumask *pmu_cpumask;
 	unsigned int scope;
 
-	cpumask_set_cpu(cpu, perf_online_mask);
-
 	/*
 	 * Early boot stage, the cpumask hasn't been set yet.
 	 * The perf_online_<domain>_masks includes the first CPU of each domain.
-	 * Always uncondifionally set the boot CPU for the perf_online_<domain>_masks.
+	 * Always unconditionally set the boot CPU for the perf_online_<domain>_masks.
 	 */
-	if (!topology_sibling_cpumask(cpu)) {
+	if (cpumask_empty(perf_online_mask)) {
 		for (scope = PERF_PMU_SCOPE_NONE + 1; scope < PERF_PMU_MAX_SCOPE; scope++) {
 			pmu_cpumask = perf_scope_cpumask(scope);
 			if (WARN_ON_ONCE(!pmu_cpumask))
 				continue;
 			cpumask_set_cpu(cpu, pmu_cpumask);
 		}
-		return;
+		goto end;
 	}
 
 	for (scope = PERF_PMU_SCOPE_NONE + 1; scope < PERF_PMU_MAX_SCOPE; scope++) {
@@ -13983,6 +13981,8 @@ static void perf_event_setup_cpumask(unsigned int cpu)
 		    cpumask_any_and(pmu_cpumask, cpumask) >= nr_cpu_ids)
 			cpumask_set_cpu(cpu, pmu_cpumask);
 	}
+end:
+	cpumask_set_cpu(cpu, perf_online_mask);
 }
 
 int perf_event_init_cpu(unsigned int cpu)
-- 
2.38.1