Re: [PATCHv2] uprobes: Use flexible array for xol_area bitmap

[Oleg Nesterov <oleg@redhat.com>]

On 05/11, Rosen Penev wrote:
>
>  struct xol_area {
>  	wait_queue_head_t		wq;		/* if all slots are busy */
> -	unsigned long			*bitmap;	/* 0 = free slot */
>
>  	struct page			*page;
>  	/*
> @@ -117,6 +116,7 @@ struct xol_area {
>  	 * the vma go away, and we must handle that reasonably gracefully.
>  	 */
>  	unsigned long			vaddr;		/* Page(s) of instruction slots */
> +	unsigned long			bitmap[];	/* 0 = free slot */
>  };
>
>  static void uprobe_warn(struct task_struct *t, const char *msg)
> @@ -1755,18 +1755,13 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
>  	struct xol_area *area;
>  	void *insns;
>
> -	area = kzalloc_obj(*area);
> +	area = kzalloc_flex(*area, bitmap, BITS_TO_LONGS(UINSNS_PER_PAGE));

The downside is that kmalloc will use kmem_cache with ->object_size = PAGE_SIZE * 2,
almost half of the allocated memory won't be used...

But technically the patch looks correct so I won't argue.

Oleg.