Re: [PATCH] x86/uv/time: Replace one-element array and save heap space

[Joe Perches <joe@perches.com>]

On Mon, 2020-05-18 at 14:01 -0500, Gustavo A. R. Silva wrote:
> The current codebase makes use of one-element arrays in the following
> form:
> 
> struct something {
>     int length;
>     u8 data[1];
> };
[]
> This issue has been out there since 2009.
> This issue was found with the help of Coccinelle and fixed _manually_.
[]
> diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
> index 7af31b245636..993a8ae6fdfb 100644
> --- a/arch/x86/platform/uv/uv_time.c
> +++ b/arch/x86/platform/uv/uv_time.c
> @@ -52,7 +52,7 @@ struct uv_rtc_timer_head {
>  	struct {
>  		int	lcpu;		/* systemwide logical cpu number */
>  		u64	expires;	/* next timer expiration for this cpu */
> -	} cpu[1];
> +	} cpu[];
>  };
>  
>  /*
> @@ -156,9 +156,8 @@ static __init int uv_rtc_allocate_timers(void)
>  		struct uv_rtc_timer_head *head = blade_info[bid];
>  
>  		if (!head) {
> -			head = kmalloc_node(sizeof(struct uv_rtc_timer_head) +
> -				(uv_blade_nr_possible_cpus(bid) *
> -					2 * sizeof(u64)),
> +			head = kmalloc_node(struct_size(head, cpu,
> +				uv_blade_nr_possible_cpus(bid)),

It's probably safer to use kzalloc_node here as well.

>  				GFP_KERNEL, nid);
>  			if (!head) {
>  				uv_rtc_deallocate_timers();