Re: [External] [PATCH] hugetlb: fix uninitialized subpool pointer

[Muchun Song]

On Wed, Feb 24, 2021 at 5:56 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> Gerald Schaefer reported a panic on s390 in hugepage_subpool_put_pages()
> with linux-next 5.12.0-20210222.
> Call trace:
>   hugepage_subpool_put_pages.part.0+0x2c/0x138
>   __free_huge_page+0xce/0x310
>   alloc_pool_huge_page+0x102/0x120
>   set_max_huge_pages+0x13e/0x350
>   hugetlb_sysctl_handler_common+0xd8/0x110
>   hugetlb_sysctl_handler+0x48/0x58
>   proc_sys_call_handler+0x138/0x238
>   new_sync_write+0x10e/0x198
>   vfs_write.part.0+0x12c/0x238
>   ksys_write+0x68/0xf8
>   do_syscall+0x82/0xd0
>   __do_syscall+0xb4/0xc8
>   system_call+0x72/0x98
>
> This is a result of the change which moved the hugetlb page subpool
> pointer from page->private to page[1]->private.  When new pages are
> allocated from the buddy allocator, the private field of the head
> page will be cleared, but the private field of subpages is not modified.
> Therefore, old values may remain.
>
> Fix by initializing hugetlb page subpool pointer in prep_new_huge_page().
>
> Fixes: f1280272ae4d ("hugetlb: use page.private for hugetlb specific page flags")
> Reported-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>

Thanks.

> ---
>  mm/hugetlb.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index c232cb67dda2..7ae5c18c98a7 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1465,6 +1465,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
>  {
>         INIT_LIST_HEAD(&page->lru);
>         set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> +       hugetlb_set_page_subpool(page, NULL);
>         set_hugetlb_cgroup(page, NULL);
>         set_hugetlb_cgroup_rsvd(page, NULL);
>         spin_lock(&hugetlb_lock);
> --
> 2.29.2
>