netdev - Re: [PATCH] net: fix race in the receive/select

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Message-ID: <87eit3l7y6.fsf@basil.nowhere.org>
Date:	Mon, 29 Jun 2009 11:12:33 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	oleg@...hat.com, eric.dumazet@...il.com
Subject: Re: [PATCH] net: fix race in the receive/select

Jiri Olsa <jolsa@...hat.com> writes:

> Adding memory barrier to the __pollwait function paired with 
> receive callbacks.  The smp_mb__after_lock define is added, 
> since {read|write|spin}_lock() on x86 are full memory barriers.

I was wondering did you see that race actually happening in practice?
If yes on which system?

At least on x86 I can't see how it happens. mb() is only a compile
time barrier and the compiler doesn't optimize over indirect callbacks
like __pollwait() anyways.

It might be still needed on some weaker ordered architectures, but did you
actually see it there?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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