Re: [PATCH v2 1/3] eal/freebsd: Do not use prev_ms_idx for hole detection

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 8/14/2025 11:32 PM, Jake Freeland wrote:
> Use rte_fbarray_is_used() to check if the previous fbarray entry is
> already empty.
> 
> Using prev_ms_idx to do this is flawed in cases where we loop through
> multiple memseg lists. Each memseg list has its own count and length,
> so using a prev_ms_idx from one memseg list to check for used entries
> in another non-empty memseg list can lead to incorrect hole placement.
> 
> Signed-off-by: Jake Freeland <jfree@FreeBSD.org>
> ---
>   lib/eal/freebsd/eal_memory.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/eal/freebsd/eal_memory.c b/lib/eal/freebsd/eal_memory.c
> index 6d3d46a390..be3bde2cb9 100644
> --- a/lib/eal/freebsd/eal_memory.c
> +++ b/lib/eal/freebsd/eal_memory.c
> @@ -103,7 +103,6 @@ rte_eal_hugepage_init(void)
>   	for (i = 0; i < internal_conf->num_hugepage_sizes; i++) {
>   		struct hugepage_info *hpi;
>   		rte_iova_t prev_end = 0;
> -		int prev_ms_idx = -1;
>   		uint64_t page_sz, mem_needed;
>   		unsigned int n_pages, max_pages;
>   
> @@ -167,9 +166,9 @@ rte_eal_hugepage_init(void)
>   				if (ms_idx < 0)
>   					continue;
>   
> -				if (need_hole && prev_ms_idx == ms_idx - 1)
> +				if (need_hole &&
> +				    rte_fbarray_is_used(arr, ms_idx - 1))
>   					ms_idx++;
> -				prev_ms_idx = ms_idx;
>   

This is not a bug as the logic won't allow for this to happen, but some 
static analysis tools might flag this:

Earlier we check for ms_idx < 0, so assuming ms_idx == 0, we will pass 
(ms_idx - 1) to rte_fbarray_is_used. This won't actually happen because 
ms_idx will never be 0 if `need_hole` is true, but *technically* it is 
not impossible, and so should probably be addressed somehow to avoid 
false positives from static analysis.

-- 
Thanks,
Anatoly