On Wed, Feb 24, 2021 at 5:43 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > 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. It seems that the buddy allocator does not initialize the private field of the tail page even when we specify __GFP_COMP. > > > 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