cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1

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 either using cgroup v1 or we're using
cgroup v2 with a mask that contains invalid CPUs. This will allow
select_fallback_rq() to figure out the mask by itself.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Link: https://lkml.kernel.org/r/20210730112443.23245-3-will@kernel.org

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 04c20de66afc2136e5bf3251b4b1780e30a1b4be..ed6ec677dd6b1c7ede8b1085bd41be28a7db479c 100644 (file)
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -15,6 +15,7 @@
 #include <linux/cpumask.h>
 #include <linux/nodemask.h>
 #include <linux/mm.h>
+#include <linux/mmu_context.h>
 #include <linux/jump_label.h>
 
 #ifdef CONFIG_CPUSETS

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index adb5190c44296b854e8bcb28d29da990031d32c5..a8693783f3855fd504c9153173efcc09c7febcf3 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3322,9 +3322,13 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 
 void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
 {
+       const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
+       const struct cpumask *cs_mask;
+
        rcu_read_lock();
-       do_set_cpus_allowed(tsk, is_in_v2_mode() ?
-               task_cs(tsk)->cpus_allowed : cpu_possible_mask);
+       cs_mask = task_cs(tsk)->cpus_allowed;
+       if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask))
+               do_set_cpus_allowed(tsk, cs_mask);
        rcu_read_unlock();
 
        /*