Vladimir Oltean <olte...@gmail.com> writes:
> The check in taprio_set_picos_per_byte is currently not robust enough
> and will trigger this division by zero, due to e.g. PHYLINK not setting
> kset->base.speed when there is no PHY connected:
>
> [ 27.109992] Division by zero in kernel.
> [ 27.113842] CPU: 1 PID: 198 Comm: tc Not tainted
> 5.3.0-rc5-01246-gc4006b8c2637-dirty #212
> [ 27.121974] Hardware name: Freescale LS1021A
> [ 27.126234] [<c03132e0>] (unwind_backtrace) from [<c030d8b8>]
> (show_stack+0x10/0x14)
> [ 27.133938] [<c030d8b8>] (show_stack) from [<c10b21b0>]
> (dump_stack+0xb0/0xc4)
> [ 27.141124] [<c10b21b0>] (dump_stack) from [<c10af97c>] (Ldiv0_64+0x8/0x18)
> [ 27.148052] [<c10af97c>] (Ldiv0_64) from [<c0700260>] (div64_u64+0xcc/0xf0)
> [ 27.154978] [<c0700260>] (div64_u64) from [<c07002d0>]
> (div64_s64+0x4c/0x68)
> [ 27.161993] [<c07002d0>] (div64_s64) from [<c0f3d890>]
> (taprio_set_picos_per_byte+0xe8/0xf4)
> [ 27.170388] [<c0f3d890>] (taprio_set_picos_per_byte) from [<c0f3f614>]
> (taprio_change+0x668/0xcec)
> [ 27.179302] [<c0f3f614>] (taprio_change) from [<c0f2bc24>]
> (qdisc_create+0x1fc/0x4f4)
> [ 27.187091] [<c0f2bc24>] (qdisc_create) from [<c0f2c0c8>]
> (tc_modify_qdisc+0x1ac/0x6f8)
> [ 27.195055] [<c0f2c0c8>] (tc_modify_qdisc) from [<c0ee9604>]
> (rtnetlink_rcv_msg+0x268/0x2dc)
> [ 27.203449] [<c0ee9604>] (rtnetlink_rcv_msg) from [<c0f4fef0>]
> (netlink_rcv_skb+0xe0/0x114)
> [ 27.211756] [<c0f4fef0>] (netlink_rcv_skb) from [<c0f4f6cc>]
> (netlink_unicast+0x1b4/0x22c)
> [ 27.219977] [<c0f4f6cc>] (netlink_unicast) from [<c0f4fa84>]
> (netlink_sendmsg+0x284/0x340)
> [ 27.228198] [<c0f4fa84>] (netlink_sendmsg) from [<c0eae5fc>]
> (sock_sendmsg+0x14/0x24)
> [ 27.235988] [<c0eae5fc>] (sock_sendmsg) from [<c0eaedf8>]
> (___sys_sendmsg+0x214/0x228)
> [ 27.243863] [<c0eaedf8>] (___sys_sendmsg) from [<c0eb015c>]
> (__sys_sendmsg+0x50/0x8c)
> [ 27.251652] [<c0eb015c>] (__sys_sendmsg) from [<c0301000>]
> (ret_fast_syscall+0x0/0x54)
> [ 27.259524] Exception stack(0xe8045fa8 to 0xe8045ff0)
> [ 27.264546] 5fa0: b6f608c8 000000f8 00000003 bed7e2f0
> 00000000 00000000
> [ 27.272681] 5fc0: b6f608c8 000000f8 004ce54c 00000128 5d3ce8c7 00000000
> 00000026 00505c9c
> [ 27.280812] 5fe0: 00000070 bed7e298 004ddd64 b6dd1e64
>
> Russell King points out that the ethtool API says zero is a valid return
> value of __ethtool_get_link_ksettings:
>
> * If it is enabled then they are read-only; if the link
> * is up they represent the negotiated link mode; if the link is down,
> * the speed is 0, %SPEED_UNKNOWN or the highest enabled speed and
> * @duplex is %DUPLEX_UNKNOWN or the best enabled duplex mode.
>
> So, it seems that taprio is not following the API... I'd suggest either
> fixing taprio, or getting agreement to change the ethtool API.
>
> The chosen path was to fix taprio.
>
> Fixes: 7b9eba7ba0c1 ("net/sched: taprio: fix picos_per_byte miscalculation")
> Signed-off-by: Vladimir Oltean <olte...@gmail.com>
> ---
Acked-by: Vinicius Costa Gomes <vinicius.go...@intel.com>
