Re: [PATCH 1/2] mm: fix bugs of mpol_rebind_nodemask()

[David Rientjes <rientjes@google.com>]

On Thu, 22 Apr 2010, Miao Xie wrote:

> - local variable might be an empty nodemask, so must be checked before setting
>   pol->v.nodes to it.
> 
> - nodes_remap() may cause the weight of pol->v.nodes being monotonic decreasing.
>   and never become large even we pass a nodemask with large weight after
>   ->v.nodes become little.
> 

That's always been the intention of rebinding a mempolicy nodemask: we 
remap the current mempolicy nodes over the new nodemask given the set of 
allowed nodes.  The nodes_remap() shouldn't be removed.

> this patch fixes these two problem.
> 
> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
> ---
>  mm/mempolicy.c |    9 ++++++---
>  1 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 08f40a2..03ba9fc 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -291,12 +291,15 @@ static void mpol_rebind_nodemask(struct mempolicy *pol,
>  	else if (pol->flags & MPOL_F_RELATIVE_NODES)
>  		mpol_relative_nodemask(&tmp, &pol->w.user_nodemask, nodes);
>  	else {
> -		nodes_remap(tmp, pol->v.nodes, pol->w.cpuset_mems_allowed,
> -			    *nodes);
> +		tmp = *nodes;
>  		pol->w.cpuset_mems_allowed = *nodes;
>  	}
>  
> -	pol->v.nodes = tmp;
> +	if (nodes_empty(tmp))
> +		pol->v.nodes = *nodes;
> +	else
> +		pol->v.nodes = tmp;
> +
>  	if (!node_isset(current->il_next, tmp)) {
>  		current->il_next = next_node(current->il_next, tmp);
>  		if (current->il_next >= MAX_NUMNODES)

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