Re: [PATCH v3] kernel/resource.c: fix stack overflow in __reserve_region_with_split

[Ram Pai <linuxram@us.ibm.com>]

On Fri, Sep 07, 2012 at 04:08:19PM -0600, T Makphaibulchoke wrote:
> Using recurvise call to try adding a non-conflicting region in the function
> __reserve_region_with_split() could result in a stack overflow in the case
> that the recursive calls are too deep.  Convert the recursive calls to
> an iterative loop to avoid the problem.
> 
> Tested on a machine containing 135 regions.  The kernel no longer panicked
> with stack overflow.
> 
> Also tested with code arbitrarily adding regions with no conflict, embedding
> two consecutive conflicts and embedding two non-consecutive conflicts.
> 
> Signed-off-by: T Makphaibulchoke <tmac@hp.com>
> 
> ---
> Change since v2:
> * Initializing both the name and flags fileds of the newly allocated region
>   request.
> 
> Change since v1:
> * Fixing __resrve_region_with_split() to ensure a reqion reserve request is
>   satisfied to the fullest extent, minus any overlapping conflicting regions.
> ---
>  kernel/resource.c |   50 ++++++++++++++++++++++++++++++++++++++------------
>  1 files changed, 38 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 34d4588..73f35d4 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -763,6 +763,7 @@ static void __init __reserve_region_with_split(struct resource *root,
>  	struct resource *parent = root;
>  	struct resource *conflict;
>  	struct resource *res = kzalloc(sizeof(*res), GFP_ATOMIC);
> +	struct resource *next_res = NULL;
> 
>  	if (!res)
>  		return;
> @@ -772,21 +773,46 @@ static void __init __reserve_region_with_split(struct resource *root,
>  	res->end = end;
>  	res->flags = IORESOURCE_BUSY;
> 
> -	conflict = __request_resource(parent, res);
> -	if (!conflict)
> -		return;
> +	while (1) {
> 
> -	/* failed, split and try again */
> -	kfree(res);
> +		conflict = __request_resource(parent, res);
> +		if (!conflict) {
> +			if (!next_res)
> +				break;
> +			res = next_res;
> +			next_res = NULL;
> +			continue;
> +		}
> 
> -	/* conflict covered whole area */
> -	if (conflict->start <= start && conflict->end >= end)
> -		return;
> +		/* conflict covered whole area */
> +		if (conflict->start <= res->start &&
> +				conflict->end >= res->end) {
> +			kfree(res);
> +			WARN_ON(next_res);
> +			break;
> +		}
> +
> +		/* failed, split and try again */
> +		if (conflict->start > res->start) {
> +			end = res->end;
> +			res->end = conflict->start - 1;
> +			if (conflict->end < end) {
> +				next_res = kzalloc(sizeof(*next_res),
> +						GFP_ATOMIC);
> +				if (!next_res) {
> +					kfree(res);
> +					break;
> +				}
> +				next_res->name = name;
> +				next_res->start = conflict->end + 1;
> +				next_res->end = end;
> +				next_res->flags = IORESOURCE_BUSY;
> +			}
> +		} else {
> +			res->start = conflict->end + 1;
> +		}
> +	}
> 
> -	if (conflict->start > start)
> -		__reserve_region_with_split(root, start, conflict->start-1, name);
> -	if (conflict->end < end)
> -		__reserve_region_with_split(root, conflict->end+1, end, name);
>  }
> 
>  void __init reserve_region_with_split(struct resource *root,

Reviewed-by: Ram Pai <linuxram@us.ibm.com>