Re: FAILED: patch "[PATCH] io_uring/kbuf: check if target buffer list is still legacy on" failed to apply to 6.12-stable tree

[Jens Axboe <axboe@kernel.dk>]

[-- Attachment #1: Type: text/plain, Size: 346 bytes --]

On 3/17/26 6:55 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.12-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Here's a tested version for 6.12.

-- 
Jens Axboe

[-- Attachment #2: 0001-io_uring-kbuf-check-if-target-buffer-list-is-still-l.patch --]
[-- Type: text/x-patch, Size: 1724 bytes --]

From d9c9b22983ade3ab50cb36ff7d5f886473963af2 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 12 Mar 2026 08:59:25 -0600
Subject: [PATCH] io_uring/kbuf: check if target buffer list is still legacy on
 recycle

Commit c2c185be5c85d37215397c8e8781abf0a69bec1f upstream.

There's a gap between when the buffer was grabbed and when it
potentially gets recycled, where if the list is empty, someone could've
upgraded it to a ring provided type. This can happen if the request
is forced via io-wq. The legacy recycling is missing checking if the
buffer_list still exists, and if it's of the correct type. Add those
checks.

Cc: stable@vger.kernel.org
Fixes: c7fb19428d67 ("io_uring: add support for ring mapped supplied buffers")
Reported-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/kbuf.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 9bd27deeee6f..25597f0629f3 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -62,9 +62,17 @@ bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags)
 
 	buf = req->kbuf;
 	bl = io_buffer_get_list(ctx, buf->bgid);
-	list_add(&buf->list, &bl->buf_list);
-	req->flags &= ~REQ_F_BUFFER_SELECTED;
+	/*
+	 * If the buffer list was upgraded to a ring-based one, or removed,
+	 * while the request was in-flight in io-wq, drop it.
+	 */
 	req->buf_index = buf->bgid;
+	if (bl && !(bl->flags & IOBL_BUF_RING))
+		list_add(&buf->list, &bl->buf_list);
+	else
+		kmem_cache_free(io_buf_cachep, buf);
+	req->flags &= ~REQ_F_BUFFER_SELECTED;
+	req->kbuf = NULL;
 
 	io_ring_submit_unlock(ctx, issue_flags);
 	return true;
-- 
2.53.0