Commit 673a5009 authored Sep 12, 2024 by Kan Liang Committed by Linus Torvalds Sep 22, 2024

perf: Fix topology_sibling_cpumask check warning on ARM

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: 4ba4f1af ("perf: Generic hotplug support for a PMU with a scope")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/lkml/20240911153854.240bbc1f@canb.auug.org.au/

Reported-by: Steven Price <steven.price@arm.com>
Closes: https://lore.kernel.org/lkml/1835eb6d-3e05-47f3-9eae-507ce165c3bf@arm.com/

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Steven Price <steven.price@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 88264981

kernel/events/core.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -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)