fs: don't randomize struct kiocb fields

This is a size sensitive structure and randomizing can introduce extra
padding that breaks io_uring's fixed size expectations. There are few
fields here as it is, half of which need a fixed order to optimally
pack, so the randomization isn't providing much.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/io-uring/b6f508ca-b1b2-5f40-7998-e4cff1cf7212@kernel.dk/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: keithbusch

include/linux/fs.h

@@ -339,17 +339,12 @@ enum rw_hint {
 
 struct kiocb {
 	struct file		*ki_filp;
-
-	/* The 'ki_filp' pointer is shared in a union for aio */
-	randomized_struct_fields_start
-
 	loff_t			ki_pos;
 	void (*ki_complete)(struct kiocb *iocb, long ret);
 	void			*private;
 	int			ki_flags;
 	u16			ki_ioprio; /* See linux/ioprio.h */
 	struct wait_page_queue	*ki_waitq; /* for async buffered IO */
-	randomized_struct_fields_end
 };
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)