On Tue 23-02-21 13:55:44, Mike Kravetz 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.
Very interesting. I have expected that the page->private would be in a
reasonable state when allocated. On the other hand hugetlb doesn't do
__GFP_COMP so tail pages are not initialized by the allocator.
> Fix by initializing hugetlb page subpool pointer in prep_new_huge_page().
>
> Fixes: f1280272ae4d ("hugetlb: use page.private for hugetlb specific page flags")
This is not a stable sha to refer to as it comes from linux next.
> Reported-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
I think this would be worth a separate patch rather than having it
folded into the original patch. Thi is really subtle.
> ---
> 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
>
--
Michal Hocko
SUSE Labs
