netdev - Re: [PATCH net-next 3/5] be2net: fix erx->rx_drops_no

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Message-ID: <1314013658.2307.21.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Mon, 22 Aug 2011 13:47:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sathya Perla <sathya.perla@...lex.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 3/5] be2net: fix erx->rx_drops_no_frags wrap
 around

Le lundi 22 août 2011 à 13:43 +0200, Eric Dumazet a écrit :

> This adds a race for lockless SNMP readers (in be_get_stats64())
> 
> They can see the 32bit value going backward.
> 
> You have to be very careful to read the *acc once, and write it once.

The "write once" is the only requirement.

Something like :

u32 newval = hi(*acc) + val;

if (wrapped)
	newval += 65536;
ACCESS_ONCE(*acc) = newval;



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