Re: [PATCH] b44: add 64 bit stats

To: Kevin Groeneveld <kgroeneveld@xxxxxxxxx>
Subject: Re: [PATCH] b44: add 64 bit stats
Cc: netdev@xxxxxxxxxxxxxxx, Simon Horman <horms@xxxxxxxxxxxx>, Julian Anastasov <ja@xxxxxx>, Wensong Zhang <wensong@xxxxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx
From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Sat, 21 Jul 2012 07:09:36 +0200
On Fri, 2012-07-20 at 22:22 -0400, Kevin Groeneveld wrote:
> On Fri, Jul 20, 2012 at 2:56 PM, Kevin Groeneveld <kgroeneveld@xxxxxxxxx> 
> wrote:
> >> In fact all network drivers should use the _bh version.
> >> Could you send a patch for all of them, based on net-next tree ?
> >
> > Sure, I can work on that.  It should be a relatively easy thing to
> > update.  I can probably send a patch within the next couple days.
> As I have been working on the patch I have been trying convince myself
> that each case I change actually needs the _bh version of the
> functions instead of blindly changing them.  So far I have found the
> following where the change seems to make sense:
> drivers/net/dummy.c
> drivers/net/ethernet/neterion/vxge/vxge-main.c
> drivers/net/loopback.c
> drivers/net/virtio_net.c
> net/bridge/br_device.c

Thats right.

> The only two other places in the networking code that use
> u64_stats_fetch_begin/u64_stats_fetch_retry are:
> net/l2tp/l2tp_netlink.c

This one is completely buggy, dont waste your time on it.

My plan for this one : dont try to have 64bit stats on 32bit arches, and
use plain "unsigned long" counters (if they are percpu), or
atomic_long_t (if they are shared by all cpus)

The writer sides might be run concurrently by several cpus, so
u64_stats_update_begin(&sstats->syncp); are racy : a reader can
be trapped forever.

> net/netfilter/ipvs/ip_vs_est.c

Same problem for this one, I think.

I CCed ipvs maintainers so that they can take a look.

> Do these need to be updated as well?  Looking at these files quickly
> and with my limited knowledge of the kernel I am not sure if they
> update the stats in a BH context or not.
> Kevin

Thanks !

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