linux-kernel - [PATCH v3 04/10] perf/arm_cspmu: Avoid placing cpumask on the stack

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Message-Id: <20240403155950.2068109-5-dawei.li@shingroup.cn>
Date: Wed,  3 Apr 2024 23:59:44 +0800
From: Dawei Li <dawei.li@...ngroup.cn>
To: will@...nel.org,
	mark.rutland@....com,
	yury.norov@...il.com,
	linux@...musvillemoes.dk
Cc: xueshuai@...ux.alibaba.com,
	renyu.zj@...ux.alibaba.com,
	yangyicong@...ilicon.com,
	jonathan.cameron@...wei.com,
	andersson@...nel.org,
	konrad.dybcio@...aro.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	Dawei Li <dawei.li@...ngroup.cn>
Subject: [PATCH v3 04/10] perf/arm_cspmu: Avoid placing cpumask on the stack

In general it's preferable to avoid placing cpumasks on the stack, as
for large values of NR_CPUS these can consume significant amounts of
stack space and make stack overflows more likely.

Use cpumask_any_and_but() to avoid the need for a temporary cpumask on
the stack.

Suggested-by: Mark Rutland <mark.rutland@....com>
Reviewed-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
---
 drivers/perf/arm_cspmu/arm_cspmu.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c b/drivers/perf/arm_cspmu/arm_cspmu.c
index b9a252272f1e..fd1004251665 100644
--- a/drivers/perf/arm_cspmu/arm_cspmu.c
+++ b/drivers/perf/arm_cspmu/arm_cspmu.c
@@ -1322,8 +1322,7 @@ static int arm_cspmu_cpu_online(unsigned int cpu, struct hlist_node *node)
 
 static int arm_cspmu_cpu_teardown(unsigned int cpu, struct hlist_node *node)
 {
-	int dst;
-	struct cpumask online_supported;
+	unsigned int dst;
 
 	struct arm_cspmu *cspmu =
 		hlist_entry_safe(node, struct arm_cspmu, cpuhp_node);
@@ -1333,9 +1332,8 @@ static int arm_cspmu_cpu_teardown(unsigned int cpu, struct hlist_node *node)
 		return 0;
 
 	/* Choose a new CPU to migrate ownership of the PMU to */
-	cpumask_and(&online_supported, &cspmu->associated_cpus,
-		    cpu_online_mask);
-	dst = cpumask_any_but(&online_supported, cpu);
+	dst = cpumask_any_and_but(&cspmu->associated_cpus,
+				  cpu_online_mask, cpu);
 	if (dst >= nr_cpu_ids)
 		return 0;
 
-- 
2.27.0