Re: hugetlb BUILD REGRESSION in linux-next20221121

On 29/11/2022 05.57, Dan Carpenter wrote:
> 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.

It seems that a reasonably clean way to deal with this, since there's
not a lot of code following the loop, is to simply move that code into
the "if (page/folio)" branch. I.e. change the tail to


   if (page) {
     free_huge_page(page); /* free it into the hugepage allocator */
     return 1;
   }
 } // this is the end of loop
 return 0;

or however it looks after the above change.

Rasmus