Re: hugetlb BUILD REGRESSION in linux-next20221121

[Dan Carpenter <error27@gmail.com>]

On Mon, Nov 28, 2022 at 02:34:54PM -0800, Sidhartha Kumar wrote:
> Hello,
> 
> One of my patches in linux-next was flagged as a Unverified Error/Warning
> with the following warning[1]:
> 
> mm/hugetlb.c:2073 alloc_pool_huge_page() error: uninitialized symbol
> 'folio'.
> 
> The relevant change is:
> 
> -    struct page *page;
> +    struct folio *folio;
>      int nr_nodes, node;
>      gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
> 
>      for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> -        page = alloc_fresh_huge_page(h, gfp_mask, node, nodes_allowed,
> -                        node_alloc_noretry);
> -        if (page)
> +        folio = alloc_fresh_hugetlb_folio(h, gfp_mask, node,
> +                    nodes_allowed, node_alloc_noretry);
> +        if (folio)
>              break;
>      }
> 
> -    if (!page)
> +    if (!folio)
> 
> It looks like I can initialize folio to NULL to avoid this error but I'm not
> sure how this would cause a regression as previously the page variable was
> unitialized as well. Please let me know if I am missing something in my
> patch or if this should be ignored.

Both the original and the new code trigger a Smatch warning.  I don't
know why the kbuild-bot marks this as a new warning.  Possibly that's
because the variable name has changed?  The kbuild-bot is run by Intel.

The problem is obviously that Smatch doesn't know that we always enter
the loop.  There are hack arounds that I could do for this, but
sometimes we dont' actually enter the loop so changing this will hide
bugs...  I am conflicted on this.

regards,
dan carpenter