On Wed, May 26, 2021 at 06:20:25PM +0200, Peter Zijlstra wrote:

On Tue, May 25, 2021 at 04:14:23PM +0100, Will Deacon wrote:

quoted

+static int restrict_cpus_allowed_ptr(struct task_struct *p,
+				     struct cpumask *new_mask,
+				     const struct cpumask *subset_mask)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+	int err;
+	struct cpumask *user_mask = NULL;
+
+	if (!p->user_cpus_ptr) {
+		user_mask = kmalloc(cpumask_size(), GFP_KERNEL);

		if (!user_mask)
			return -ENOMEM;
	}

?

We won't blow up if we continue without user_mask here, but I agree that
it's more straightforward to return an error and have
force_compatible_cpus_allowed_ptr() noisily override the mask.

We're in pretty deep trouble if we're failing this allocation anyway.

Will