Subject: [PATCH v4 09/14] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1

From: Will Deacon <[email-masked]>
Date: Tue, 24 Nov 2020 15:50:34 +0000

If the scheduler cannot find an allowed CPU for a task,
cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask
if cgroup v1 is in use.

In preparation for allowing architectures to provide their own fallback
mask, just return early if we're not using cgroup v2 and allow
select_fallback_rq() to figure out the mask by itself.

Cc: Li Zefan <[email-masked]>
Cc: Tejun Heo <[email-masked]>
Cc: Johannes Weiner <[email-masked]>
Reviewed-by: Quentin Perret <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
---
 kernel/cgroup/cpuset.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 57b5b5d0a5fd..e970737c3ed2 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3299,9 +3299,11 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 
 void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
+	if (!is_in_v2_mode())
+		return; /* select_fallback_rq will try harder */
+
 	rcu_read_lock();
-	do_set_cpus_allowed(tsk, is_in_v2_mode() ?
-		task_cs(tsk)->cpus_allowed : cpu_possible_mask);
+	do_set_cpus_allowed(tsk, task_cs(tsk)->cpus_allowed);
 	rcu_read_unlock();
 
 	/*
-- 
2.29.2.454.gaff20da3a2-goog

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