[PATCH 1/2] io_uring: don't do opcode prep twice

[Pavel Begunkov <asml.silence@gmail.com>]

Calling into opcode prep handlers may be dangerous, as they re-read
SQE but might not re-initialise requests completely. If io_req_defer()
passed fast checks and is done with preparations, punt it async.

As all other cases are covered with nulling @sqe, this guarantees that
io_[opcode]_prep() are visited only once per request.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index cda729de4ea3..bb356c56f57c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5438,7 +5438,8 @@ static int io_req_defer(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	if (!req_need_defer(req, seq) && list_empty(&ctx->defer_list)) {
 		spin_unlock_irq(&ctx->completion_lock);
 		kfree(de);
-		return 0;
+		io_queue_async_work(req);
+		return -EIOCBQUEUED;
 	}
 
 	trace_io_uring_defer(ctx, req, req->user_data);
-- 
2.24.0