[PATCH 09/11] io_uring: prepare fixed rw for dynanic buffers

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

With dynamic buffer updates, registered buffers in the table may change
at any moment. First of all we want to prevent future races between
updating and importing (i.e. io_import_fixed()), where the latter one
may happen without uring_lock held, e.g. from io-wq.

A second problem is that currently we may do importing several times for
IORING_OP_{READ,WRITE}_FIXED, e.g. getting -EAGAIN on an inline attempt
and then redoing import after apoll/from iowq. In this case it can see
two completely different buffers, that's not good, especially since we
often hide short reads from the userspace.

Copy iter when going async. There are concerns about performance.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index cff8561d567a..c80b5fef159d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -903,6 +903,7 @@ static const struct io_op_def io_op_defs[] = {
 		.unbound_nonreg_file	= 1,
 		.pollin			= 1,
 		.plug			= 1,
+		.needs_async_setup	= 1,
 		.async_size		= sizeof(struct io_async_rw),
 	},
 	[IORING_OP_WRITE_FIXED] = {
@@ -911,6 +912,7 @@ static const struct io_op_def io_op_defs[] = {
 		.unbound_nonreg_file	= 1,
 		.pollout		= 1,
 		.plug			= 1,
+		.needs_async_setup	= 1,
 		.async_size		= sizeof(struct io_async_rw),
 	},
 	[IORING_OP_POLL_ADD] = {
@@ -2683,6 +2685,10 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 		kiocb->ki_complete = io_complete_rw;
 	}
 
+	if (req->opcode == IORING_OP_READ_FIXED ||
+	    req->opcode == IORING_OP_WRITE_FIXED)
+		io_req_set_rsrc_node(req);
+
 	req->rw.addr = READ_ONCE(sqe->addr);
 	req->rw.len = READ_ONCE(sqe->len);
 	req->buf_index = READ_ONCE(sqe->buf_index);
@@ -5919,7 +5925,9 @@ static int io_req_prep_async(struct io_kiocb *req)
 
 	switch (req->opcode) {
 	case IORING_OP_READV:
+	case IORING_OP_READ_FIXED:
 		return io_rw_prep_async(req, READ);
+	case IORING_OP_WRITE_FIXED:
 	case IORING_OP_WRITEV:
 		return io_rw_prep_async(req, WRITE);
 	case IORING_OP_SENDMSG:
-- 
2.31.1