netdev - ndo_get_stats and rtnl

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Date:	Sun, 9 Sep 2012 18:23:16 +0300
From:	Shlomo Pongartz <shlomop@...lanox.com>
To:	<netdev@...r.kernel.org>
Subject: ndo_get_stats and rtnl_netlink

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...

Regards
Shlomo Pongratz
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