io_uring: fix early fdput() of file

A previous commit shuffled some code around, and inadvertently used
struct file after fdput() had been called on it. As we can't touch
the file post fdput() dropping our reference, move the fdput() to
after that has been done.

Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/io-uring/YPnqM0fY3nM5RdRI@zeniv-ca.linux.org.uk/
Fixes: f2a48dd0 ("io_uring: refactor io_sq_offload_create()")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -7991,10 +7991,12 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 		f = fdget(p->wq_fd);
 		if (!f.file)
 			return -ENXIO;
+		if (f.file->f_op != &io_uring_fops) {
 			fdput(f);
-		if (f.file->f_op != &io_uring_fops)
 			return -EINVAL;
 		}
+		fdput(f);
+	}
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		struct task_struct *tsk;
 		struct io_sq_data *sqd;