Re: [PATCH] powerpc: Add write barrier before enabling DTL flags

[Michael Ellerman <michael@ellerman.id.au>]

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On Tue, 2009-03-24 at 13:55 +1100, Jeremy Kerr wrote:
> Currently, we don't enforce any ordering for updates to the lppaca
> when enabling dtl logging, so we may end up enabling logging before the
> index fields have been established.
> 
> This change adds a smp_wmb() before doing the actual enable.
> 
> Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
> 
> ---
>  arch/powerpc/platforms/pseries/dtl.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/dtl.c b/arch/powerpc/platforms/pseries/dtl.c
> index dc9b0f8..fafcaa0 100644
> --- a/arch/powerpc/platforms/pseries/dtl.c
> +++ b/arch/powerpc/platforms/pseries/dtl.c
> @@ -107,6 +107,10 @@ static int dtl_enable(struct dtl *dtl)
>  	/* set our initial buffer indices */
>  	dtl->last_idx = lppaca[dtl->cpu].dtl_idx = 0;
>  
> +	/* ensure that our updates to the lppaca fields have occurred before
> +	 * we actually enable the logging */
> +	smp_wmb();

Wouldn't this still be a problem on a UP kernel?

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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