linux-kernel - [PATCH -next] sched/fair: Fix task migrated to isolated cpus

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Date: Fri, 1 Mar 2024 02:31:09 +0000
From: Zheng Zucheng <zhengzucheng@...wei.com>
To: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<bristot@...hat.com>, <vschneid@...hat.com>, <wuyun.abel@...edance.com>,
	<joshdon@...gle.com>
CC: <linux-kernel@...r.kernel.org>
Subject: [PATCH -next] sched/fair: Fix task migrated to isolated cpus

On the wakeup path with hyperthreading, select cpu only looks at
task->cpus_ptr to see if the task can run on the target cpu. If isolcpus
kernel parameter is set, and isolated cpus will be part of mask
task->cpus_ptr, tasks were migrated to our isolated cpus.

Steps to reproduce on my 32-CPU hyperthreads machine:
1. with boot parameter: "isolcpus=0,1"
   (thread lists: 0,16 and 1,17)
2. cgcreate -g cpuset:test
   echo 0-31 > /sys/fs/cgroup/cpuset/test/cpuset.cpus
   echo 0 > /sys/fs/cgroup/cpuset/test/cpuset.mems
   cgexec -g cpuset:test "test_threads"
3. some threads will be migrated to the isolated cpu0/1.

Fix it by checking the valid domain mask in select_idle_smt() and
select_idle_core()

Fixes: 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
Fixes: 3e6efe87cd5c ("sched/fair: Remove redundant check in select_idle_smt()")
Cc: stable@...r.kernel.org # v5.12+
Signed-off-by: Zheng Zucheng <zhengzucheng@...wei.com>
---
 kernel/sched/fair.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 533547e3c90a..e6552c77e0f1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7289,7 +7289,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 		if (!available_idle_cpu(cpu)) {
 			idle = false;
 			if (*idle_cpu == -1) {
-				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
+				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, cpus)) {
 					*idle_cpu = cpu;
 					break;
 				}
@@ -7297,7 +7297,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 			}
 			break;
 		}
-		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
+		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, cpus))
 			*idle_cpu = cpu;
 	}
 
@@ -7311,12 +7311,12 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
 /*
  * Scan the local SMT mask for idle CPUs.
  */
-static int select_idle_smt(struct task_struct *p, int target)
+static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
 {
 	int cpu;
 
 	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
-		if (cpu == target)
+		if (cpu == target || !cpumask_test_cpu(cpu, sched_domain_span(sd)))
 			continue;
 		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
 			return cpu;
@@ -7341,7 +7341,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
 	return __select_idle_cpu(core, p);
 }
 
-static inline int select_idle_smt(struct task_struct *p, int target)
+static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
 {
 	return -1;
 }
@@ -7591,7 +7591,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 		has_idle_core = test_idle_cores(target);
 
 		if (!has_idle_core && cpus_share_cache(prev, target)) {
-			i = select_idle_smt(p, prev);
+			i = select_idle_smt(p, sd, prev);
 			if ((unsigned int)i < nr_cpumask_bits)
 				return i;
 		}
-- 
2.34.1