[PATCH] sched_ext: Use atomic cpumask_clear_cpu in scx_idle_test_and_clear_cpu()

[Michal Blaszczyk]

In scx_idle_test_and_clear_cpu(), the shared idle_smts mask is modified
locklessly by concurrent CPUs. Currently, the code uses
__cpumask_clear_cpu() to clear a CPU from the mask. Because this is
a non-atomic read-modify-write operation, concurrent modifications to
different bits within the same memory word can lead to data races and
lost updates.

Fix this by replacing __cpumask_clear_cpu() with the atomic
cpumask_clear_cpu().

Fixes: 48849271e661 ("sched_ext: idle: Per-node idle cpumasks")
Signed-off-by: Michal Blaszczyk <michalblk@xxxxxxxxxx>
---
 kernel/sched/ext/idle.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/ext/idle.c b/kernel/sched/ext/idle.c
index d2973fb3af6d..8985b48c83a5 100644
--- a/kernel/sched/ext/idle.c
+++ b/kernel/sched/ext/idle.c
@@ -104,7 +104,7 @@ static bool scx_idle_test_and_clear_cpu(int cpu)
 		if (cpumask_intersects(smt, idle_smts))
 			cpumask_andnot(idle_smts, idle_smts, smt);
 		else if (cpumask_test_cpu(cpu, idle_smts))
-			__cpumask_clear_cpu(cpu, idle_smts);
+			cpumask_clear_cpu(cpu, idle_smts);
 	}
 
 	return cpumask_test_and_clear_cpu(cpu, idle_cpus);
-- 
2.55.0.897.gb25b4bd76c-goog