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io_uring/net: inherit IORING_CQE_F_BUF_MORE across bundle recv retries

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When a bundle recv retries inside io_recv_finish(), the merge logic OR
the saved cflags from the previous iteration with the cflags returned by
the new iteration:
  cflags = req->cqe.flags | (cflags & CQE_F_MASK);

Bits listed in CQE_F_MASK are inherited from the new iteration, and all
other bits (notably IORING_CQE_F_BUFFER and the buffer ID) come from the
saved cflags. Before this change CQE_F_MASK covered only
IORING_CQE_F_SOCK_NONEMPTY and IORING_CQE_F_MORE.

When using provided buffer rings (IOU_PBUF_RING_INC) with incremental
mode, and bundle recv, io_kbuf_inc_commit() can leave the head ring
entry partially consumed, __io_put_kbufs() then sets
IORING_CQE_F_BUF_MORE on the returned cflags so userspace knows the
buffer ID will be reused for subsequent completions.

Because IORING_CQE_F_BUF_MORE was not in CQE_F_MASK, the merge above
silently dropped it whenever the final retry iteration partially
consumed the buffer, and the subsequent req->cqe.flags = cflags &
~CQE_F_MASK save would have left a stale IORING_CQE_F_BUF_MORE in the
carried-over cflags had one been present. Userspace would then
wrongfully advance it ring head past an entry the kernel still uses.

Add IORING_CQE_F_BUF_MORE to CQE_F_MASK so it is both inherited from the
new iteration into the user-visible CQE and stripped from the saved
cflags between iterations.

Cc: stable@vger.kernel.org
Signed-off-by: Clément Léger <cleger@meta.com>
Assisted-by: Claude:claude-opus-4.6
Fixes: ae98dbf43d ("io_uring/kbuf: add support for incremental buffer consumption")
Link: https://patch.msgid.link/20260604160715.2482972-1-cleger@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Clément Léger 2026-06-04 09:07:13 -07:00 committed by Jens Axboe
parent a88c02915d
commit ed46f39c47
1 changed files with 2 additions and 1 deletions
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3
io_uring/net.c
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@ -842,7 +842,8 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
}
/* bits to clear in old and inherit in new cflags on bundle retry */
#define CQE_F_MASK (IORING_CQE_F_SOCK_NONEMPTY|IORING_CQE_F_MORE)
#define CQE_F_MASK (IORING_CQE_F_SOCK_NONEMPTY|IORING_CQE_F_MORE|\
IORING_CQE_F_BUF_MORE)
/*
* Finishes io_recv and io_recvmsg.