io_uring: don't check PF_EXITING from syscall

io_sq_thread_acquire_mm_files() can find a PF_EXITING task only when
it's called from task_work context. Don't check it in all other cases,
that are when we're in io_uring_enter().
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1213,8 +1213,6 @@ static int __io_sq_thread_acquire_mm_files(struct io_ring_ctx *ctx,
 static inline int io_sq_thread_acquire_mm_files(struct io_ring_ctx *ctx,
 						struct io_kiocb *req)
 {
-	if (unlikely(current->flags & PF_EXITING))
-		return -EFAULT;
 	if (!(ctx->flags & IORING_SETUP_SQPOLL))
 		return 0;
 	return __io_sq_thread_acquire_mm_files(ctx, req);
@@ -2338,7 +2336,8 @@ static void __io_req_task_submit(struct io_kiocb *req)
 
 	/* ctx stays valid until unlock, even if we drop all ours ctx->refs */
 	mutex_lock(&ctx->uring_lock);
-	if (!ctx->sqo_dead && !io_sq_thread_acquire_mm_files(ctx, req))
+	if (!ctx->sqo_dead && !(current->flags & PF_EXITING) &&
+	    !io_sq_thread_acquire_mm_files(ctx, req))
 		__io_queue_sqe(req);
 	else
 		__io_req_task_cancel(req, -EFAULT);