tee: optee: add might_sleep for RPC requests

If the kernel is compiled with CONFIG_PREEMPT_VOLUNTARY and OP-TEE is
executing a long running workload, the following errors are raised:

[ 1705.971228] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[ 1705.977195] rcu:     (detected by 0, t=2102 jiffies, g=51977, q=3)
[ 1705.983152] rcu: All QSes seen, last rcu_sched kthread activity 2102 (140596-138494), jiffies_till_next_fqs=1, root ->qsmask 0x0
[ 1705.994729] optee-xtest     R  running task        0   169    157 0x00000002

While OP-TEE is returning regularly to the kernel due to timer
interrupts, the OPTEE_SMC_FUNC_FOREIGN_INTR case does not contain an
explicit rescheduling point. Add a might_sleep() to the RPC request case
to ensure that the kernel can reschedule another task if OP-TEE requests
RPC handling.

Signed-off-by: Rouven Czerwinski <[email protected]>
Signed-off-by: Jens Wiklander <[email protected]>

drivers/tee/optee/call.c

@@ -148,6 +148,7 @@ u32 optee_do_call_with_arg(struct tee_context *ctx, phys_addr_t parg)
 			 */
 			optee_cq_wait_for_completion(&optee->call_queue, &w);
 		} else if (OPTEE_SMC_RETURN_IS_RPC(res.a0)) {
+			might_sleep();
 			param.a0 = res.a0;
 			param.a1 = res.a1;
 			param.a2 = res.a2;