io_uring: grab RCU read lock marking task run

Not required right now, as io_req_local_work_add() already calls this
helper with the RCU read lock held. But in preparation for that not
being the case, grab it locally.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/tw.c

@@ -158,11 +158,11 @@ void tctx_task_work(struct callback_head *cb)
  */
 static void io_ctx_mark_taskrun(struct io_ring_ctx *ctx)
 {
-	lockdep_assert_in_rcu_read_lock();
-
 	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) {
-		struct io_rings *rings = rcu_dereference(ctx->rings_rcu);
+		struct io_rings *rings;
 
+		guard(rcu)();
+		rings = rcu_dereference(ctx->rings_rcu);
 		atomic_or(IORING_SQ_TASKRUN, &rings->sq_flags);
 	}
 }