io_uring/register: don't get a reference to the registered ring fd

This isn't necessary and was only done because the register path isn't a
hot path and hence the extra ref/put doesn't matter, and to have the
exit path be able to unconditionally put whatever file was gotten
regardless of the type.

In preparation for sharing this code with the main io_uring_enter(2)
syscall, drop the reference and have the caller conditionally put the
file if it was a normal file descriptor.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/register.c

@@ -941,7 +941,8 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 /*
  * Given an 'fd' value, return the ctx associated with if. If 'registered' is
  * true, then the registered index is used. Otherwise, the normal fd table.
- * Caller must call fput() on the returned file, unless it's an ERR_PTR.
+ * Caller must call fput() on the returned file if it isn't a registered file,
+ * unless it's an ERR_PTR.
  */
 struct file *io_uring_register_get_file(unsigned int fd, bool registered)
 {
@@ -958,8 +959,6 @@ struct file *io_uring_register_get_file(unsigned int fd, bool registered)
 			return ERR_PTR(-EINVAL);
 		fd = array_index_nospec(fd, IO_RINGFD_REG_MAX);
 		file = tctx->registered_rings[fd];
-		if (file)
-			get_file(file);
 	} else {
 		file = fget(fd);
 	}
@@ -1038,6 +1037,7 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
 				ctx->buf_table.nr, ret);
 	mutex_unlock(&ctx->uring_lock);
 
-	fput(file);
+	if (!use_registered_ring)
+		fput(file);
 	return ret;
 }

io_uring/rsrc.c

@@ -1291,7 +1291,8 @@ out:
 	if (src_ctx != ctx)
 		mutex_unlock(&src_ctx->uring_lock);
 
-	fput(file);
+	if (!registered_src)
+		fput(file);
 	return ret;
 }