netdev - Re: ndo_get_stats and rtnl

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Date:	Mon, 10 Sep 2012 11:09:49 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shlomo Pongartz <shlomop@...lanox.com>
Cc:	netdev@...r.kernel.org
Subject: Re: ndo_get_stats and rtnl_netlink

On Sun, 2012-09-09 at 18:23 +0300, Shlomo Pongartz wrote:
> Hi,
> 
> Just realized that dev_get_stats which calls into a netdevice 
> ndo_get_stats64/ndo_get_stats can be
> called with or without RTNL lock protection. If called from 
> rtnl_fill_ifinfo e.g as of invocation of
> "ip link show <interface>, there IS locking, however if called from 
> dev_seq_printf_stats e.g as of
> invocation of reading the /sys/class/net/<interface>/statistics/ 
> entries, etc more cases -- no locking.
> 
> This turned to be problematic when implementing the ethtool 
> "set_channels" directive which
> changes the number of **rings**, since we stepped on a bug where the 
> rings data structure was
> changed by the ethtool flow in the same time a statistics call was done 
> into the driver, etc.
> 
> What would be the way to continue here, per driver lock sounds non 
> generic...

RTNL locking is not needed to fetch stats, and would be overkill.

Each driver has its own way to protect/gather its stats.



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