io_uring: rework io_uring_enter to simplify return value

io_uring_enter returns the count submitted preferrably over an error
code. In some code paths this check is not required, so reorganise the
code so that the check is only done as needed.
This is also a prep for returning error codes only in waiting scenarios.
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220421091345.2115755-4-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -10872,7 +10872,6 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		size_t, argsz)
 {
 	struct io_ring_ctx *ctx;
-	int submitted = 0;
 	struct fd f;
 	long ret;
 
@@ -10935,15 +10934,15 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 			if (ret)
 				goto out;
 		}
-		submitted = to_submit;
+		ret = to_submit;
 	} else if (to_submit) {
 		ret = io_uring_add_tctx_node(ctx);
 		if (unlikely(ret))
 			goto out;
 
 		mutex_lock(&ctx->uring_lock);
-		submitted = io_submit_sqes(ctx, to_submit);
-		if (submitted != to_submit) {
+		ret = io_submit_sqes(ctx, to_submit);
+		if (ret != to_submit) {
 			mutex_unlock(&ctx->uring_lock);
 			goto out;
 		}
@@ -10952,6 +10951,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 		mutex_unlock(&ctx->uring_lock);
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
+		int ret2;
 		if (ctx->syscall_iopoll) {
 			/*
 			 * We disallow the app entering submit/complete with
@@ -10961,22 +10961,29 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 			 */
 			mutex_lock(&ctx->uring_lock);
 iopoll_locked:
-			ret = io_validate_ext_arg(flags, argp, argsz);
-			if (likely(!ret)) {
-				min_complete = min(min_complete, ctx->cq_entries);
-				ret = io_iopoll_check(ctx, min_complete);
+			ret2 = io_validate_ext_arg(flags, argp, argsz);
+			if (likely(!ret2)) {
+				min_complete = min(min_complete,
+						   ctx->cq_entries);
+				ret2 = io_iopoll_check(ctx, min_complete);
 			}
 			mutex_unlock(&ctx->uring_lock);
 		} else {
 			const sigset_t __user *sig;
 			struct __kernel_timespec __user *ts;
 
-			ret = io_get_ext_arg(flags, argp, &argsz, &ts, &sig);
-			if (unlikely(ret))
-				goto out;
-			min_complete = min(min_complete, ctx->cq_entries);
-			ret = io_cqring_wait(ctx, min_complete, sig, argsz, ts);
+			ret2 = io_get_ext_arg(flags, argp, &argsz, &ts, &sig);
+			if (likely(!ret2)) {
+				min_complete = min(min_complete,
+						   ctx->cq_entries);
+				ret2 = io_cqring_wait(ctx, min_complete, sig,
+						      argsz, ts);
+			}
 		}
+
+		if (!ret)
+			ret = ret2;
+
 	}
 
 out:
@@ -10984,7 +10991,7 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 out_fput:
 	if (!(flags & IORING_ENTER_REGISTERED_RING))
 		fdput(f);
-	return submitted ? submitted : ret;
+	return ret;
 }
 
 #ifdef CONFIG_PROC_FS