linux-kernel - Re: [PATCH] synchronize

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Message-ID: <20071019055333.GA10748@gondor.apana.org.au>
Date:	Fri, 19 Oct 2007 13:53:33 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] synchronize_irq needs a barrier

On Fri, Oct 19, 2007 at 02:26:54PM +1000, Benjamin Herrenschmidt wrote:
>
> I think a simple smp_mb(); here after foo = 1; is enough, which means
> basically just having an smp_mp(); inside napi_synchronize(), before
> the test_bit(). Or do I miss something ?

Yes I think you're right.  In this case we do have barriers
everywhere else so this should work.

Although if you want napi_synchronize to have the property that
when it returns all NAPI processing effects are visible then
you'd need another smp_mb() after the loop.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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