net_sched: fix skb memory leak in deferred qdisc drops

net_sched: fix skb memory leak in deferred qdisc drops

When the network stack cleans up the deferred list via qdisc_run_end(),
it operates on the root qdisc. If the root qdisc do not implement the
TCQ_F_DEQUEUE_DROPS flag the packets queue to free are never freed and
gets stranded on the child's local to_free list.

Fix this by making qdisc_dequeue_drop() aware of the root qdisc. It
fetches the root qdisc and check for the TCQ_F_DEQUEUE_DROPS flag. If
the flag is present, the packet is appended directly to the root's
to_free list. Otherwise, drop it directly as it was done before the
optimization was implemented.

Fixes: a6efc273ab82 ("net_sched: use qdisc_dequeue_drop() in cake, codel, fq_codel")
Reported-by: Damilola Bello <damilola@aterlo.com>
Closes: https://lore.kernel.org/netdev/CAPgFtOLaedBMU0f_BxV2bXftTJSmJr018Q5uozOo5vVo6b9tjw@mail.gmail.com/
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260408100044.4530-1-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>