io_uring/sqpoll: do not put cpumask on stack

Putting the cpumask on the stack is deprecated for a long time (since
2d3854a3), as these can be big. Given that, change the on-stack
allocation of allowed_mask to be dynamically allocated.

Fixes: f011c9cf ("io_uring/sqpoll: do not allow pinning outside of cpuset")
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Link: https://lore.kernel.org/r/20240916111150.1266191-1-felix.moessbauer@siemens.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/sqpoll.c

@@ -461,15 +461,22 @@ __cold int io_sq_offload_create(struct io_ring_ctx *ctx,
 			return 0;
 
 		if (p->flags & IORING_SETUP_SQ_AFF) {
-			struct cpumask allowed_mask;
+			cpumask_var_t allowed_mask;
 			int cpu = p->sq_thread_cpu;
 
 			ret = -EINVAL;
 			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 				goto err_sqpoll;
-			cpuset_cpus_allowed(current, &allowed_mask);
-			if (!cpumask_test_cpu(cpu, &allowed_mask))
+			ret = -ENOMEM;
+			if (!alloc_cpumask_var(&allowed_mask, GFP_KERNEL))
 				goto err_sqpoll;
+			ret = -EINVAL;
+			cpuset_cpus_allowed(current, allowed_mask);
+			if (!cpumask_test_cpu(cpu, allowed_mask)) {
+				free_cpumask_var(allowed_mask);
+				goto err_sqpoll;
+			}
+			free_cpumask_var(allowed_mask);
 			sqd->sq_cpu = cpu;
 		} else {
 			sqd->sq_cpu = -1;