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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Jamal Hadi Salim , Cong Wang , Jiri Pirko , Vinicius Costa Gomes , linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org, Muhammad Husaini Zulkifli , Peilin Ye , Pedro Tammela Subject: [PATCH RESEND net-next 2/5] net/sched: taprio: keep child Qdisc refcount elevated at 2 in offload mode Date: Fri, 2 Jun 2023 13:37:47 +0300 Message-Id: <20230602103750.2290132-3-vladimir.oltean@nxp.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230602103750.2290132-1-vladimir.oltean@nxp.com> References: <20230602103750.2290132-1-vladimir.oltean@nxp.com> X-ClientProxiedBy: BE1P281CA0095.DEUP281.PROD.OUTLOOK.COM (2603:10a6:b10:79::10) To AM0PR04MB6452.eurprd04.prod.outlook.com (2603:10a6:208:16d::21) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AM0PR04MB6452:EE_|PAXPR04MB8926:EE_ X-MS-Office365-Filtering-Correlation-Id: 87f51ae4-859a-40ef-2f3e-08db63557b07 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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In the software scheduling case, taprio attaches itself to all TXQs, thus having a refcount of 1 + the number of TX queues. In this mode, q->qdiscs[] is not visible directly to the Qdisc API. The lifetime of the Qdiscs from this private array lasts until qdisc_destroy() -> taprio_destroy(). In the fully offloaded case, the root taprio has a refcount of 1, and all child q->qdiscs[] also have a refcount of 1. The child q->qdiscs[] are visible to the Qdisc API (they are attached to the netdev TXQs directly), however taprio loses a reference to them very early - during qdisc_graft(parent==NULL) -> taprio_attach(). At that time, taprio frees the q->qdiscs[] array to not leak memory, but interestingly, it does not release a reference on these qdiscs because it doesn't effectively own them - they are created by taprio but owned by the Qdisc core, and will be freed by qdisc_graft(parent==NULL, new==NULL) -> qdisc_put(old) when the Qdisc is deleted or when the child Qdisc is replaced with something else. My interest is to change this equilibrium such that taprio also owns a reference on the q->qdiscs[] child Qdiscs for the lifetime of the root Qdisc, including in full offload mode. I want this because I would like taprio_leaf(), taprio_dump_class(), taprio_dump_class_stats() to have insight into q->qdiscs[] for the software scheduling mode - currently they look at dev_queue->qdisc_sleeping, which is, as mentioned, the same as the root taprio. The following set of changes is necessary: - don't free q->qdiscs[] early in taprio_attach(), free it late in taprio_destroy() for consistency with software mode. But: - currently that's not possible, because taprio doesn't own a reference on q->qdiscs[]. So hold that reference - once during the initial attach() and once during subsequent graft() calls when the child is changed. - always keep track of the current child in q->qdiscs[], even for full offload mode, so that we free in taprio_destroy() what we should, and not something stale. Signed-off-by: Vladimir Oltean --- net/sched/sch_taprio.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index b1c611c72aa4..8807fc915b79 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -2138,23 +2138,20 @@ static void taprio_attach(struct Qdisc *sch) qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT; old = dev_graft_qdisc(dev_queue, qdisc); + /* Keep refcount of q->qdiscs[ntx] at 2 */ + qdisc_refcount_inc(qdisc); } else { /* In software mode, attach the root taprio qdisc * to all netdev TX queues, so that dev_qdisc_enqueue() * goes through taprio_enqueue(). */ old = dev_graft_qdisc(dev_queue, sch); + /* Keep root refcount at 1 + num_tx_queues */ qdisc_refcount_inc(sch); } if (old) qdisc_put(old); } - - /* access to the child qdiscs is not needed in offload mode */ - if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { - kfree(q->qdiscs); - q->qdiscs = NULL; - } } static struct netdev_queue *taprio_queue_get(struct Qdisc *sch, @@ -2183,15 +2180,24 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, if (dev->flags & IFF_UP) dev_deactivate(dev); - if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { + /* In software mode, the root taprio qdisc is still the one attached to + * all netdev TX queues, and hence responsible for taprio_enqueue() to + * forward the skbs to the child qdiscs from the private q->qdiscs[] + * array. So only attach the new qdisc to the netdev queue in offload + * mode, where the enqueue must bypass taprio. However, save the + * reference to the new qdisc in the private array in both cases, to + * have an up-to-date reference to our children. + */ + if (FULL_OFFLOAD_IS_ENABLED(q->flags)) *old = dev_graft_qdisc(dev_queue, new); - } else { + else *old = q->qdiscs[cl - 1]; - q->qdiscs[cl - 1] = new; - } - if (new) + q->qdiscs[cl - 1] = new; + if (new) { + qdisc_refcount_inc(new); new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT; + } if (dev->flags & IFF_UP) dev_activate(dev);