On Fri, Jun 26, 2026 at 1:16 PM Victor Nogueira [off-list ref] wrote:

On 25/06/2026 06:51, Bryam Vargas via B4 Relay wrote:

quoted

From: Bryam Vargas <redacted>

When taprio's software path peeks a non-work-conserving child qdisc, the
child stashes the peeked skb in its gso_skb; taprio_dequeue_from_txq()
then takes the packet with a direct child ->dequeue() call, which ignores
that stash, orphans the peeked skb and desyncs the child's qlen/backlog.
With a qfq child this re-enters the child on an emptied list and
dereferences NULL, panicking the kernel from softirq on ordinary egress.

Take the packet through qdisc_dequeue_peeked(), as sch_red and sch_sfb
now do. The helper returns the child's stashed skb first and is a no-op
when there is none, so a work-conserving child is unaffected and the
gated path now consumes the skb whose length was charged to the budget.

Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
Cc: stable@vger.kernel.org
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Bryam Vargas <redacted>

Reviewed-by: Victor Nogueira <redacted>

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

cheers,
jamal