Subject: Re: [PATCH net] af_packet: set defaule value for tmo

From: walter harms <[email-masked]>
Date: Mon, 09 Dec 2019 15:14:23 +0100

Am 09.12.2019 14:31, schrieb Mao Wenan:
> There is softlockup when using TPACKET_V3:
> ...
> NMI watchdog: BUG: soft lockup - CPU#2 stuck for 60010ms!
> (__irq_svc) from [<c0558a0c>] (_raw_spin_unlock_irqrestore+0x44/0x54)
> (_raw_spin_unlock_irqrestore) from [<c027b7e8>] (mod_timer+0x210/0x25c)
> (mod_timer) from [<c0549c30>]
> (prb_retire_rx_blk_timer_expired+0x68/0x11c)
> (prb_retire_rx_blk_timer_expired) from [<c027a7ac>]
> (call_timer_fn+0x90/0x17c)
> (call_timer_fn) from [<c027ab6c>] (run_timer_softirq+0x2d4/0x2fc)
> (run_timer_softirq) from [<c021eaf4>] (__do_softirq+0x218/0x318)
> (__do_softirq) from [<c021eea0>] (irq_exit+0x88/0xac)
> (irq_exit) from [<c0240130>] (msa_irq_exit+0x11c/0x1d4)
> (msa_irq_exit) from [<c0209cf0>] (handle_IPI+0x650/0x7f4)
> (handle_IPI) from [<c02015bc>] (gic_handle_irq+0x108/0x118)
> (gic_handle_irq) from [<c0558ee4>] (__irq_usr+0x44/0x5c)
> ...
> 
> If __ethtool_get_link_ksettings() is failed in
> prb_calc_retire_blk_tmo(), msec and tmo will be zero, so tov_in_jiffies
> is zero and the timer expire for retire_blk_timer is turn to
> mod_timer(&pkc->retire_blk_timer, jiffies + 0),
> which will trigger cpu usage of softirq is 100%.
> 
> Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
> Tested-by: Xiao Jiangfeng <[email-masked]>
> Signed-off-by: Mao Wenan <[email-masked]>
> ---
>  net/packet/af_packet.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 53c1d41fb1c9..118cd66b7516 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -544,7 +544,8 @@ static int prb_calc_retire_blk_tmo(struct packet_sock *po,
>  			msec = 1;
>  			div = ecmd.base.speed / 1000;
>  		}
> -	}
> +	} else
> +		return DEFAULT_PRB_RETIRE_TOV;
>  
>  	mbits = (blk_size_in_bytes * 8) / (1024 * 1024);
>  

With some litrle refactoring you can save one indent
and make it more readable.

err = __ethtool_get_settings(dev, &ecmd);

if (err)
     return DEFAULT_PRB_RETIRE_TOV;

speed = ethtool_cmd_speed(&ecmd);

if (speed < SPEED_1000 || speed == SPEED_UNKNOWN)
      return DEFAULT_PRB_RETIRE_TOV;

msec = 1;  // never changes - needed at all ??
div = speed / 1000;

jm2c

re,
 wh