[PATCH 6.18 065/212] io_uring/kbuf: propagate BUF_MORE through early buffer commit path

Greg Kroah-Hartman
2026-03-23T14:04:14Z

From: Jens Axboe <axboe@kernel.dk>

commit 418eab7a6f3c002d8e64d6e95ec27118017019af upstream.

When io_should_commit() returns true (eg for non-pollable files), buffer
commit happens at buffer selection time and sel->buf_list is set to
NULL. When __io_put_kbufs() generates CQE flags at completion time, it
calls __io_put_kbuf_ring() which finds a NULL buffer_list and hence
cannot determine whether the buffer was consumed or not. This means that
IORING_CQE_F_BUF_MORE is never set for non-pollable input with
incrementally consumed buffers.

Likewise for io_buffers_select(), which always commits upfront and
discards the return value of io_kbuf_commit().

Add REQ_F_BUF_MORE to store the result of io_kbuf_commit() during early
commit. Then __io_put_kbuf_ring() can check this flag and set
IORING_F_BUF_MORE accordingy.

Reported-by: Martin Michaelis <code@mgjm.de>
Cc: stable@vger.kernel.org
Fixes: ae98dbf43d75 ("io_uring/kbuf: add support for incremental buffer consumption")
Link: https://github.com/axboe/liburing/issues/1553
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/io_uring_types.h | 3 +++
io_uring/kbuf.c | 10 +++++++---
2 files changed, 10 insertions(+), 3 deletions(-)

--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -518,6 +518,7 @@ enum {
REQ_F_BL_NO_RECYCLE_BIT,
REQ_F_BUFFERS_COMMIT_BIT,
REQ_F_BUF_NODE_BIT,
+ REQ_F_BUF_MORE_BIT,
REQ_F_HAS_METADATA_BIT,
REQ_F_IMPORT_BUFFER_BIT,
REQ_F_SQE_COPIED_BIT,
@@ -603,6 +604,8 @@ enum {
REQ_F_BUFFERS_COMMIT = IO_REQ_FLAG(REQ_F_BUFFERS_COMMIT_BIT),
/* buf node is valid */
REQ_F_BUF_NODE = IO_REQ_FLAG(REQ_F_BUF_NODE_BIT),
+ /* incremental buffer consumption, more space available */
+ REQ_F_BUF_MORE = IO_REQ_FLAG(REQ_F_BUF_MORE_BIT),
/* request has read/write metadata assigned */
REQ_F_HAS_METADATA = IO_REQ_FLAG(REQ_F_HAS_METADATA_BIT),
/*
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -216,7 +216,8 @@ static struct io_br_sel io_ring_buffer_s
sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));

if (io_should_commit(req, issue_flags)) {
- io_kbuf_commit(req, sel.buf_list, *len, 1);
+ if (!io_kbuf_commit(req, sel.buf_list, *len, 1))
+ req->flags |= REQ_F_BUF_MORE;
sel.buf_list = NULL;
}
return sel;
@@ -349,7 +350,8 @@ int io_buffers_select(struct io_kiocb *r
*/
if (ret > 0) {
req->flags |= REQ_F_BUFFERS_COMMIT | REQ_F_BL_NO_RECYCLE;
- io_kbuf_commit(req, sel->buf_list, arg->out_len, ret);
+ if (!io_kbuf_commit(req, sel->buf_list, arg->out_len, ret))
+ req->flags |= REQ_F_BUF_MORE;
}
} else {
ret = io_provided_buffers_select(req, &arg->out_len, sel->buf_list, arg->iovs);
@@ -395,8 +397,10 @@ static inline bool __io_put_kbuf_ring(st

if (bl)
ret = io_kbuf_commit(req, bl, len, nr);
+ if (ret && (req->flags & REQ_F_BUF_MORE))
+ ret = false;

- req->flags &= ~REQ_F_BUFFER_RING;
+ req->flags &= ~(REQ_F_BUFFER_RING | REQ_F_BUF_MORE);
return ret;
}