Re: [PATCH] : bug fix in multipath drr code.

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

On Mon, May 23, 2005 at 05:56:39PM +0530, pravin wrote:
>  AFAIU, there is a race condition in multipath_drr code,
> these code paths try to access & change last_selection variable
> without any synchronization.

Yes you're right.
 
> Index: linux-2.6.12-rc4/net/ipv4/multipath_drr.c
> ===================================================================
> --- linux-2.6.12-rc4.orig/net/ipv4/multipath_drr.c    2005-05-06 
> 22:20:31.000000000 -0700
> +++ linux-2.6.12-rc4/net/ipv4/multipath_drr.c 2005-05-22 06:41:39.000000000 
> -0700
> @@ -145,11 +145,13 @@
>       int cur_min_devidx = -1;
>  
>               /* if necessary and possible utilize the old alternative */
> -     if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 &&
> -         last_selection != NULL) {
> -             result = last_selection;
> -             *rp = result;
> -             return;
> +     if ((flp->flags & FLOWI_FLAG_MULTIPATHOLDROUTE) != 0 ) {
> +             struct rtable *last_result = last_selection;
> +             if(last_result != NULL &&
> +                multipath_comparekeys(&last_result->fl, flp)) {
> +                     *rp = last_result;
> +                     return;
> +             }
>       }

You don't need all this code.  All you need to do is do
result = last_selection before the if condition and then
check result in the if condition instead of last_selection.

The multipath_comparekeys isn't necessary either.

Cheers,
-- 
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