io_uring/rw: move fixed buffer import to issue path

Registered buffers may depend on a linked command, which makes the prep
path too early to import. Move to the issue path when the node is
actually needed like all the other users of fixed buffers.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20250227223916.143006-3-kbusch@meta.com
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/opdef.c

@@ -104,7 +104,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.iopoll_queue		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_read_fixed,
-		.issue			= io_read,
+		.issue			= io_read_fixed,
 	},
 	[IORING_OP_WRITE_FIXED] = {
 		.needs_file		= 1,
@@ -118,7 +118,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.iopoll_queue		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_write_fixed,
-		.issue			= io_write,
+		.issue			= io_write_fixed,
 	},
 	[IORING_OP_POLL_ADD] = {
 		.needs_file		= 1,

io_uring/rw.c

@@ -357,31 +357,30 @@ int io_prep_writev(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return io_prep_rwv(req, sqe, ITER_SOURCE);
 }
 
-static int io_prep_rw_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+static int io_init_rw_fixed(struct io_kiocb *req, unsigned int issue_flags,
 			    int ddir)
 {
 	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
-	struct io_async_rw *io;
+	struct io_async_rw *io = req->async_data;
 	int ret;
 
-	ret = __io_prep_rw(req, sqe, ddir);
-	if (unlikely(ret))
-		return ret;
+	if (io->bytes_done)
+		return 0;
 
-	io = req->async_data;
-	ret = io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir, 0);
+	ret = io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir,
+				issue_flags);
 	iov_iter_save_state(&io->iter, &io->iter_state);
 	return ret;
 }
 
 int io_prep_read_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw_fixed(req, sqe, ITER_DEST);
+	return __io_prep_rw(req, sqe, ITER_DEST);
 }
 
 int io_prep_write_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
-	return io_prep_rw_fixed(req, sqe, ITER_SOURCE);
+	return __io_prep_rw(req, sqe, ITER_SOURCE);
 }
 
 /*
@@ -1147,6 +1146,28 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
 	}
 }
 
+int io_read_fixed(struct io_kiocb *req, unsigned int issue_flags)
+{
+	int ret;
+
+	ret = io_init_rw_fixed(req, issue_flags, ITER_DEST);
+	if (unlikely(ret))
+		return ret;
+
+	return io_read(req, issue_flags);
+}
+
+int io_write_fixed(struct io_kiocb *req, unsigned int issue_flags)
+{
+	int ret;
+
+	ret = io_init_rw_fixed(req, issue_flags, ITER_SOURCE);
+	if (unlikely(ret))
+		return ret;
+
+	return io_write(req, issue_flags);
+}
+
 void io_rw_fail(struct io_kiocb *req)
 {
 	int res;

io_uring/rw.h

@@ -38,6 +38,8 @@ int io_prep_read(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_prep_write(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_read(struct io_kiocb *req, unsigned int issue_flags);
 int io_write(struct io_kiocb *req, unsigned int issue_flags);
+int io_read_fixed(struct io_kiocb *req, unsigned int issue_flags);
+int io_write_fixed(struct io_kiocb *req, unsigned int issue_flags);
 void io_readv_writev_cleanup(struct io_kiocb *req);
 void io_rw_fail(struct io_kiocb *req);
 void io_req_rw_complete(struct io_kiocb *req, io_tw_token_t tw);