From 6e773b5161506a4d0e739eb3aa4667d28f20219c Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Thu, 15 Oct 2026 19:31:00 +0000 Subject: [PATCH] io_uring/kbuf: handle index wrap in last buffer check io_ring_buffer_select() flags the request with REQ_F_BL_EMPTY if it takes the last buffer of the ring. Head and tail are 16-bit counters, but "head + 1" is computed as an int. If head is 65535 and tail has wrapped to 0, that compares 65536 to 0 and the flag isn't set. A bundle receive relies on the flag to tell that there is no point in trying to get more data. Without it, it goes for another round, finds no buffer, and the request, which has received data, is marked as failed on account of the -ENOBUFS. That severs a link, and ends a multishot. Fixes: c3f9109dbc9e ("io_uring/kbuf: flag request if buffer pool is empty after buffer pick") Assisted-by: LLM Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-36-c1556f5d7bf5@toxicpanda.com Signed-off-by: Jens Axboe --- io_uring/kbuf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c index 6e2facf34bfa..c9641b6ccc8f 100644 --- a/io_uring/kbuf.c +++ b/io_uring/kbuf.c @@ -204,7 +204,7 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len, if (unlikely(tail == head)) return sel; - if (head + 1 == tail) + if ((__u16)(head + 1) == tail) req->flags |= REQ_F_BL_EMPTY; buf = io_ring_head_to_buf(br, head, bl->mask);