On 09/12/2017 02:38 PM, Eric Dumazet wrote:
> On Tue, 2017-09-12 at 13:14 -0700, Florian Fainelli wrote:
>> We can enter a deadlock situation because there is no sufficient protection
>> when ndo_get_stats64() runs in process context to guard against RX or TX NAPI
>> contexts running in softirq, this can lead to the following lockdep splat and
>> actual deadlock was experienced as well with an iperf session in the
>> background
>> and a while loop doing ifconfig + ethtool.
>
>> So just remove the u64_stats_update_begin()/end() pair in ndo_get_stats64()
>> since it does not appear to be useful for anything. No inconsistency was
>> observed with either ifconfig or ethtool, global TX counts equal the sum of
>> per-queue TX counts on a 32-bit architecture.
>>
>> Fixes: 10377ba7673d ("net: systemport: Support 64bit statistics")
>> Signed-off-by: Florian Fainelli <f.faine...@gmail.com>
>> ---
>> drivers/net/ethernet/broadcom/bcmsysport.c | 3 ---
>> 1 file changed, 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/broadcom/bcmsysport.c
>> b/drivers/net/ethernet/broadcom/bcmsysport.c
>> index a6572b51435a..c3c53f6cd9e6 100644
>> --- a/drivers/net/ethernet/broadcom/bcmsysport.c
>> +++ b/drivers/net/ethernet/broadcom/bcmsysport.c
>> @@ -1735,11 +1735,8 @@ static void bcm_sysport_get_stats64(struct net_device
>> *dev,
>> stats->tx_packets += tx_packets;
>> }
>>
>> - /* lockless update tx_bytes and tx_packets */
>> - u64_stats_update_begin(&priv->syncp);
>
> Yes, this u64_stats_update_begin()/u64_stats_update_end() is bogus
>
> But why do we even write on tx_bytes/tx_packets here ???
That's for the ethtool -S netdev stats copy (that's on me, I added that
in the driver initial version), so yes, not very robust...
>
> Seems very wrong anyway.
>
> (ethtool -S does not call bcm_sysport_get_stats64() to refresh them )
Yes that might actually be the simplest way to get this fixed.
>
>> stats64->tx_bytes = stats->tx_bytes;
>> stats64->tx_packets = stats->tx_packets;
>> - u64_stats_update_end(&priv->syncp);
>>
>> do {
>> start = u64_stats_fetch_begin_irq(&priv->syncp);
>
>
--
Florian
