linux-kernel - [tip: perf/urgent] perf/core: Fix topology_sibling

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Message-ID: <172710515461.2215.10614315030535616389.tip-bot2@tip-bot2>
Date: Mon, 23 Sep 2024 15:25:54 -0000
From: "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Stephen Rothwell <sfr@...b.auug.org.au>,
 Steven Price <steven.price@....com>, Kan Liang <kan.liang@...ux.intel.com>,
 Ingo Molnar <mingo@...nel.org>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/core: Fix topology_sibling_cpumask() check
 warning on ARM

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     4e340f66f76b36003646165130fd7e3de5219d7f
Gitweb:        https://git.kernel.org/tip/4e340f66f76b36003646165130fd7e3de5219d7f
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Thu, 12 Sep 2024 07:50:25 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 19 Sep 2024 11:51:50 +02:00

perf/core: Fix topology_sibling_cpumask() check warning on ARM

The following 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 will
never be NULL.

To work around the warning, 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 <sfr@...b.auug.org.au>
Reported-by: Steven Price <steven.price@....com>
Tested-by: Steven Price <steven.price@....com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20240912145025.1574448-1-kan.liang@linux.intel.com
---
 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 4f03eb9..c5b4fba 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -14002,21 +14002,19 @@ 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++) {
@@ -14031,6 +14029,8 @@ 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)