From db46e3a88a09c5cf7e505664d01da7238cd56c92 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Thu, 15 Sep 2022 13:08:01 +0300 Subject: [PATCH 1/2] net/sched: taprio: avoid disabling offload when it was never enabled In an incredibly strange API design decision, qdisc->destroy() gets called even if qdisc->init() never succeeded, not exclusively since commit 87b60cfacf9f ("net_sched: fix error recovery at qdisc creation"), but apparently also earlier (in the case of qdisc_create_dflt()). The taprio qdisc does not fully acknowledge this when it attempts full offload, because it starts off with q->flags = TAPRIO_FLAGS_INVALID in taprio_init(), then it replaces q->flags with TCA_TAPRIO_ATTR_FLAGS parsed from netlink (in taprio_change(), tail called from taprio_init()). But in taprio_destroy(), we call taprio_disable_offload(), and this determines what to do based on FULL_OFFLOAD_IS_ENABLED(q->flags). But looking at the implementation of FULL_OFFLOAD_IS_ENABLED() (a bitwise check of bit 1 in q->flags), it is invalid to call this macro on q->flags when it contains TAPRIO_FLAGS_INVALID, because that is set to U32_MAX, and therefore FULL_OFFLOAD_IS_ENABLED() will return true on an invalid set of flags. As a result, it is possible to crash the kernel if user space forces an error between setting q->flags = TAPRIO_FLAGS_INVALID, and the calling of taprio_enable_offload(). This is because drivers do not expect the offload to be disabled when it was never enabled. The error that we force here is to attach taprio as a non-root qdisc, but instead as child of an mqprio root qdisc: $ tc qdisc add dev swp0 root handle 1: \ mqprio num_tc 8 map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 hw 0 $ tc qdisc replace dev swp0 parent 1:1 \ taprio num_tc 8 map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 base-time 0 \ sched-entry S 0x7f 990000 sched-entry S 0x80 100000 \ flags 0x0 clockid CLOCK_TAI Unable to handle kernel paging request at virtual address fffffffffffffff8 [fffffffffffffff8] pgd=0000000000000000, p4d=0000000000000000 Internal error: Oops: 96000004 [#1] PREEMPT SMP Call trace: taprio_dump+0x27c/0x310 vsc9959_port_setup_tc+0x1f4/0x460 felix_port_setup_tc+0x24/0x3c dsa_slave_setup_tc+0x54/0x27c taprio_disable_offload.isra.0+0x58/0xe0 taprio_destroy+0x80/0x104 qdisc_create+0x240/0x470 tc_modify_qdisc+0x1fc/0x6b0 rtnetlink_rcv_msg+0x12c/0x390 netlink_rcv_skb+0x5c/0x130 rtnetlink_rcv+0x1c/0x2c Fix this by keeping track of the operations we made, and undo the offload only if we actually did it. I've added "bool offloaded" inside a 4 byte hole between "int clockid" and "atomic64_t picos_per_byte". Now the first cache line looks like below: $ pahole -C taprio_sched net/sched/sch_taprio.o struct taprio_sched { struct Qdisc * * qdiscs; /* 0 8 */ struct Qdisc * root; /* 8 8 */ u32 flags; /* 16 4 */ enum tk_offsets tk_offset; /* 20 4 */ int clockid; /* 24 4 */ bool offloaded; /* 28 1 */ /* XXX 3 bytes hole, try to pack */ atomic64_t picos_per_byte; /* 32 0 */ /* XXX 8 bytes hole, try to pack */ spinlock_t current_entry_lock; /* 40 0 */ /* XXX 8 bytes hole, try to pack */ struct sched_entry * current_entry; /* 48 8 */ struct sched_gate_list * oper_sched; /* 56 8 */ /* --- cacheline 1 boundary (64 bytes) --- */ Fixes: 9c66d1564676 ("taprio: Add support for hardware offloading") Signed-off-by: Vladimir Oltean Reviewed-by: Vinicius Costa Gomes Signed-off-by: Jakub Kicinski --- net/sched/sch_taprio.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 0b941dd63d268..9bec73019f94b 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -67,6 +67,7 @@ struct taprio_sched { u32 flags; enum tk_offsets tk_offset; int clockid; + bool offloaded; atomic64_t picos_per_byte; /* Using picoseconds because for 10Gbps+ * speeds it's sub-nanoseconds per byte */ @@ -1279,6 +1280,8 @@ static int taprio_enable_offload(struct net_device *dev, goto done; } + q->offloaded = true; + done: taprio_offload_free(offload); @@ -1293,12 +1296,9 @@ static int taprio_disable_offload(struct net_device *dev, struct tc_taprio_qopt_offload *offload; int err; - if (!FULL_OFFLOAD_IS_ENABLED(q->flags)) + if (!q->offloaded) return 0; - if (!ops->ndo_setup_tc) - return -EOPNOTSUPP; - offload = taprio_offload_alloc(0); if (!offload) { NL_SET_ERR_MSG(extack, @@ -1314,6 +1314,8 @@ static int taprio_disable_offload(struct net_device *dev, goto out; } + q->offloaded = false; + out: taprio_offload_free(offload); From 1461d212ab277d8bba1a753d33e9afe03d81f9d4 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Thu, 15 Sep 2022 13:08:02 +0300 Subject: [PATCH 2/2] net/sched: taprio: make qdisc_leaf() see the per-netdev-queue pfifo child qdiscs taprio can only operate as root qdisc, and to that end, there exists the following check in taprio_init(), just as in mqprio: if (sch->parent != TC_H_ROOT) return -EOPNOTSUPP; And indeed, when we try to attach taprio to an mqprio child, it fails as expected: $ tc qdisc add dev swp0 root handle 1: mqprio num_tc 8 \ map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 hw 0 $ tc qdisc replace dev swp0 parent 1:2 taprio num_tc 8 \ map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \ base-time 0 sched-entry S 0x7f 990000 sched-entry S 0x80 100000 \ flags 0x0 clockid CLOCK_TAI Error: sch_taprio: Can only be attached as root qdisc. (extack message added by me) But when we try to attach a taprio child to a taprio root qdisc, surprisingly it doesn't fail: $ tc qdisc replace dev swp0 root handle 1: taprio num_tc 8 \ map 0 1 2 3 4 5 6 7 queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \ base-time 0 sched-entry S 0x7f 990000 sched-entry S 0x80 100000 \ flags 0x0 clockid CLOCK_TAI $ tc qdisc replace dev swp0 parent 1:2 taprio num_tc 8 \ map 0 1 2 3 4 5 6 7 \ queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 \ base-time 0 sched-entry S 0x7f 990000 sched-entry S 0x80 100000 \ flags 0x0 clockid CLOCK_TAI This is because tc_modify_qdisc() behaves differently when mqprio is root, vs when taprio is root. In the mqprio case, it finds the parent qdisc through p = qdisc_lookup(dev, TC_H_MAJ(clid)), and then the child qdisc through q = qdisc_leaf(p, clid). This leaf qdisc q has handle 0, so it is ignored according to the comment right below ("It may be default qdisc, ignore it"). As a result, tc_modify_qdisc() goes through the qdisc_create() code path, and this gives taprio_init() a chance to check for sch_parent != TC_H_ROOT and error out. Whereas in the taprio case, the returned q = qdisc_leaf(p, clid) is different. It is not the default qdisc created for each netdev queue (both taprio and mqprio call qdisc_create_dflt() and keep them in a private q->qdiscs[], or priv->qdiscs[], respectively). Instead, taprio makes qdisc_leaf() return the _root_ qdisc, aka itself. When taprio does that, tc_modify_qdisc() goes through the qdisc_change() code path, because the qdisc layer never finds out about the child qdisc of the root. And through the ->change() ops, taprio has no reason to check whether its parent is root or not, just through ->init(), which is not called. The problem is the taprio_leaf() implementation. Even though code wise, it does the exact same thing as mqprio_leaf() which it is copied from, it works with different input data. This is because mqprio does not attach itself (the root) to each device TX queue, but one of the default qdiscs from its private array. In fact, since commit 13511704f8d7 ("net: taprio offload: enforce qdisc to netdev queue mapping"), taprio does this too, but just for the full offload case. So if we tried to attach a taprio child to a fully offloaded taprio root qdisc, it would properly fail too; just not to a software root taprio. To fix the problem, stop looking at the Qdisc that's attached to the TX queue, and instead, always return the default qdiscs that we've allocated (and to which we privately enqueue and dequeue, in software scheduling mode). Since Qdisc_class_ops :: leaf is only called from tc_modify_qdisc(), the risk of unforeseen side effects introduced by this change is minimal. Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler") Signed-off-by: Vladimir Oltean Reviewed-by: Vinicius Costa Gomes Signed-off-by: Jakub Kicinski --- net/sched/sch_taprio.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 9bec73019f94b..86675a79da1e4 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -1951,12 +1951,14 @@ static int taprio_dump(struct Qdisc *sch, struct sk_buff *skb) static struct Qdisc *taprio_leaf(struct Qdisc *sch, unsigned long cl) { - struct netdev_queue *dev_queue = taprio_queue_get(sch, cl); + struct taprio_sched *q = qdisc_priv(sch); + struct net_device *dev = qdisc_dev(sch); + unsigned int ntx = cl - 1; - if (!dev_queue) + if (ntx >= dev->num_tx_queues) return NULL; - return dev_queue->qdisc_sleeping; + return q->qdiscs[ntx]; } static unsigned long taprio_find(struct Qdisc *sch, u32 classid)