[PATCH 1/3] io_uring: pass sqe for link head

[Pavel Begunkov <asml.silence@xxxxxxxxx>]

Save an sqe for a head of a link, so it doesn't go through switch in
io_req_defer_prep() nor allocating an async context in advance.

Also, it's fixes potenial memleak for double-preparing head requests.
E.g. prep in io_submit_sqe() and then prep in io_req_defer(),
which leaks iovec for vectored read/writes.

Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
 fs/io_uring.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index f00c2c9c67c0..e18056af5672 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4721,20 +4721,22 @@ static void io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	}
 }
 
-static inline void io_queue_link_head(struct io_kiocb *req)
+static inline void io_queue_link_head(struct io_kiocb *req,
+				      const struct io_uring_sqe *sqe)
 {
 	if (unlikely(req->flags & REQ_F_FAIL_LINK)) {
 		io_cqring_add_event(req, -ECANCELED);
 		io_double_put_req(req);
 	} else
-		io_queue_sqe(req, NULL);
+		io_queue_sqe(req, sqe);
 }
 
 #define SQE_VALID_FLAGS	(IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK|	\
 				IOSQE_IO_HARDLINK | IOSQE_ASYNC)
 
 static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-			  struct io_submit_state *state, struct io_kiocb **link)
+			  struct io_submit_state *state, struct io_kiocb **link,
+			  const struct io_uring_sqe **link_sqe)
 {
 	const struct cred *old_creds = NULL;
 	struct io_ring_ctx *ctx = req->ctx;
@@ -4812,7 +4814,7 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
 		/* last request of a link, enqueue the link */
 		if (!(sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK))) {
-			io_queue_link_head(head);
+			io_queue_link_head(head, *link_sqe);
 			*link = NULL;
 		}
 	} else {
@@ -4823,10 +4825,8 @@ static bool io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		if (sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) {
 			req->flags |= REQ_F_LINK;
 			INIT_LIST_HEAD(&req->link_list);
-			ret = io_req_defer_prep(req, sqe);
-			if (ret)
-				req->flags |= REQ_F_FAIL_LINK;
 			*link = req;
+			*link_sqe = sqe;
 		} else {
 			io_queue_sqe(req, sqe);
 		}
@@ -4924,6 +4924,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 	struct io_kiocb *link = NULL;
 	int i, submitted = 0;
 	bool mm_fault = false;
+	const struct io_uring_sqe *link_sqe = NULL;
 
 	/* if we have a backlog and couldn't flush it all, return BUSY */
 	if (test_bit(0, &ctx->sq_check_overflow)) {
@@ -4983,7 +4984,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 		req->needs_fixed_file = async;
 		trace_io_uring_submit_sqe(ctx, req->opcode, req->user_data,
 						true, async);
-		if (!io_submit_sqe(req, sqe, statep, &link))
+		if (!io_submit_sqe(req, sqe, statep, &link, &link_sqe))
 			break;
 	}
 
@@ -4993,7 +4994,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
 		percpu_ref_put_many(&ctx->refs, nr - ref_used);
 	}
 	if (link)
-		io_queue_link_head(link);
+		io_queue_link_head(link, link_sqe);
 	if (statep)
 		io_submit_state_end(&state);
 
-- 
2.24.0