Re: [PATCH] hugetlb: Fix __prep_compound_gigantic_page page flag setting

[Miaohe Lin]

On 2022/11/19 3:52, Mike Kravetz wrote:
> Commit 2b21624fc232 ("hugetlb: freeze allocated pages before creating
> hugetlb pages") changed the order page flags were cleared and set in the
> head page.  It moved the __ClearPageReserved after __SetPageHead.
> However, there is a check to make sure __ClearPageReserved is never
> done on a head page.  If CONFIG_DEBUG_VM_PGFLAGS is enabled, the
> following BUG will be hit when creating a hugetlb gigantic page:
> 
>     page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
>     ------------[ cut here ]------------
>     kernel BUG at include/linux/page-flags.h:500!
>     Call Trace will differ depending on whether hugetlb page is created
>     at boot time or run time.
> 
> Make sure to __ClearPageReserved BEFORE __SetPageHead.
> 
> Reported-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Fixes: 2b21624fc232 ("hugetlb: freeze allocated pages before creating hugetlb pages")
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Yes, PG_reserved is PF_NO_COMPOUND policy. Thanks for fixing this.

Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>

Thanks,
Miaohe Lin