On 2022/3/4 16:28, HORIGUCHI NAOYA(堀口 直也) wrote: > On Mon, Feb 28, 2022 at 10:02:45PM +0800, Miaohe Lin wrote: >> The huge zero page could reach here and if we ever try to split it, the >> VM_BUG_ON_PAGE will be triggered in split_huge_page_to_list(). Also the >> non-lru compound movable pages could be taken for transhuge pages. Skip >> these pages by checking PageLRU because huge zero page isn't lru page as >> non-lru compound movable pages. > > It seems that memory_failure() also fails at get_any_page() with "hwpoison: > unhandlable page" message. > > [16478.203474] page:00000000b6acdbd1 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1810b4 > [16478.206612] flags: 0x57ffffc0801000(reserved|hwpoison|node=1|zone=2|lastcpupid=0x1fffff) > [16478.209411] raw: 0057ffffc0801000 fffff11bc6042d08 fffff11bc6042d08 0000000000000000 > [16478.211921] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000 > [16478.214473] page dumped because: hwpoison: unhandlable page > [16478.216386] Memory failure: 0x1810b4: recovery action for unknown page: Ignored > > We can't handle errors on huge (or normal) zero page, so the current Sorry for confusing commit log again. I should have a coffee before I make this patch. Huge or normal zero page will fail at get_any_page because they're neither HWPoisonHandlable nor PageHuge. > behavior seems to me more suitable than "unsplit thp". > > Or if you have some producer to reach the following path with huge zero > page, could you share it? > What I mean is that non-lru movable compound page can reach here unexpected because __PageMovable(page) is handleable now. So get_any_page could succeed to grab the page refcnt. And since it's compound page, it will go through the split_huge_page_to_list because PageTransHuge checks PageHead(page) which can also be true for compound page. But this type of pages is unexpected for split_huge_page_to_list. Does this make sense for you? Thanks Naoya. > Thanks, > Naoya Horiguchi > >> >> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >> --- >> mm/memory-failure.c | 14 ++++++++++++++ >> 1 file changed, 14 insertions(+) >> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index 23bfd809dc8c..ac6492e36978 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1792,6 +1792,20 @@ int memory_failure(unsigned long pfn, int flags) >> } >> >> if (PageTransHuge(hpage)) { >> + /* >> + * The non-lru compound movable pages could be taken for >> + * transhuge pages. Also huge zero page could reach here >> + * and if we ever try to split it, the VM_BUG_ON_PAGE will >> + * be triggered in split_huge_page_to_list(). Skip these >> + * pages by checking PageLRU because huge zero page isn't >> + * lru page as non-lru compound movable pages. >> + */ >> + if (!PageLRU(hpage)) { >> + put_page(p); >> + action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED); >> + res = -EBUSY; >> + goto unlock_mutex; >> + } >> /* >> * The flag must be set after the refcount is bumped >> * otherwise it may race with THP split. >> -- >> 2.23.0