FAILED: patch "[PATCH] io_uring/kbuf: check if target buffer list is still legacy on" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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 <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x c2c185be5c85d37215397c8e8781abf0a69bec1f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026031701-humid-ultimate-853d@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c2c185be5c85d37215397c8e8781abf0a69bec1f Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Thu, 12 Mar 2026 08:59:25 -0600
Subject: [PATCH] io_uring/kbuf: check if target buffer list is still legacy on
recycle

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.

index dae5b4ab3819..e7f444953dfb 100644
@@ -111,9 +111,18 @@ 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);
-	bl->nbufs++;
+	/*
+	 * 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->flags & IOBL_BUF_RING)) {
+		list_add(&buf->list, &bl->buf_list);
+		bl->nbufs++;
+	} else {
+		kfree(buf);
+	}
 	req->flags &= ~REQ_F_BUFFER_SELECTED;
+	req->kbuf = NULL;
 
 	io_ring_submit_unlock(ctx, issue_flags);
 	return true;

Here's one for 6.6-stable.

Jens Axboe

From e0dd02979a6f1ca378fb173d5e36dd591ee8ef3f Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
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.

---
 io_uring/kbuf.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

index b2c381634393..ad1e14359662 100644
@@ -70,9 +70,15 @@ 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->is_mapped)
+		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

Now applied, thanks.

greg k-h