Re: FAILED: patch "[PATCH] io_uring/kbuf: check if target buffer list is still legacy on" failed to apply to 6.1-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 3/17/26 6:55 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.1-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 one for 6.1-stable.

-- 
Jens Axboe

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From 35660c08085dad169e708326998a50ef59aefcbc 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 | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index d18fe3996ddb..70a44d8ef094 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -69,9 +69,15 @@ void 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);
+	/*
+	 * If the buffer list was upgraded to a ring-based one, or removed,
+	 * while the request was in-flight in io-wq, drop it.
+	 */
+	if (bl && !bl->buf_nr_pages)
+		list_add(&buf->list, &bl->buf_list);
 	req->flags &= ~REQ_F_BUFFER_SELECTED;
 	req->buf_index = buf->bgid;
+	req->kbuf = NULL;
 
 	io_ring_submit_unlock(ctx, issue_flags);
 	return;
-- 
2.53.0