Messages in this thread | | | From | Vinicius Costa Gomes <> | Subject | Re: [PATCH v2 net 1/2] net/sched: taprio: avoid disabling offload when it was never enabled | Date | Thu, 15 Sep 2022 14:52:29 -0700 |
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Vladimir Oltean <vladimir.oltean@nxp.com> writes:
> 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 <vladimir.oltean@nxp.com> > ---
Reviewed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Cheers, -- Vinicius
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