> On Aug 30, 2023, at 05:37, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> Currently, vmemmap optimization of hugetlb pages is performed before the
> hugetlb flag (previously hugetlb destructor) is set identifying it as a
> hugetlb folio. This means there is a window of time where an ordinary
> folio does not have all associated vmemmap present. The core mm only
> expects vmemmap to be potentially optimized for hugetlb and device dax.
> This can cause problems in code such as memory error handling that may
> want to write to tail struct pages.
>
> There is only one call to perform hugetlb vmemmap optimization today.
> To fix this issue, simply set the hugetlb flag before that call.
>
> There was a similar issue in the free hugetlb path that was previously
> addressed. The two routines that optimize or restore hugetlb vmemmap
> should only be passed hugetlb folios/pages. To catch any callers not
> following this rule, add VM_WARN_ON calls to the routines. In the
> hugetlb free code paths, some calls could be made to restore vmemmap
> after clearing the hugetlb flag. This was 'safe' as in these cases
> vmemmap was already present and the call was a NOOP. However, for
> consistency these calls where eliminated so that we can add the
> VM_WARN_ON checks.
>
> Fixes: f41f2ed43ca5 ("mm: hugetlb: free the vmemmap pages associated with each HugeTLB page")
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Thanks for your fix.
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
