Re: [PATCH v5 0/6] MR1628: ntdll: Implement Low Fragmentation Heap.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about dlls/ntdll/heap.c:
> +{
> - const char *blocks = (char *)(group + 1);
> - block->base_offset = ((char *)block - blocks) / block_size;
>
> +}
> -
>
> +static inline struct block *group_get_block( struct group *group, SIZE_T block_size, UINT index )
> +{
> - char *blocks = (char *)(group + 1);
> - return (struct block *)(blocks + index * block_size);
>
> +}
> -
>
> +/* lookup a free block using the group free_bits, the current thread must own the group */
> +static inline LONG group_find_free_block( struct group *group, SIZE_T block_size, struct block **block )
> +{
> +#if defined(__GNUC__) && ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)))
> - int i = __builtin_ffs( group->free_bits ) - 1;

Technically, this constitutes a data race since we're accessing a shared variable (concurrent access from `heap_free_block_lfh`) without volatile semantics.  You should at least mark it volatile and load it to a local variable explicitly.