On Thu 08-09-22 11:25:54, Miaohe Lin wrote: > On 2022/9/8 11:06, HORIGUCHI NAOYA(堀口 直也) wrote: > > On Thu, Sep 08, 2022 at 10:19:03AM +0800, Miaohe Lin wrote: > >> On 2022/9/7 20:11, Naoya Horiguchi wrote: > > ... > >>> >From 8a5c284df732943065d23838090d15c94cd10395 Mon Sep 17 00:00:00 2001 > >>> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> > >>> Date: Wed, 7 Sep 2022 20:58:44 +0900 > >>> Subject: [PATCH] mm/huge_memory: use pfn_to_online_page() in > >>> split_huge_pages_all() > >>> > >>> NULL pointer dereference is triggered when calling thp split via debugfs > >>> on the system with offlined memory blocks. With debug option enabled, > >>> the following kernel messages are printed out: > >>> > >>> page:00000000467f4890 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x121c000 > >>> flags: 0x17fffc00000000(node=0|zone=2|lastcpupid=0x1ffff) > >>> raw: 0017fffc00000000 0000000000000000 dead000000000122 0000000000000000 > >>> raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000 > >>> page dumped because: unmovable page > >>> page:000000007d7ab72e is uninitialized and poisoned > >>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) > >>> ------------[ cut here ]------------ > >>> kernel BUG at include/linux/mm.h:1248! > >>> invalid opcode: 0000 [#1] PREEMPT SMP PTI > >>> CPU: 16 PID: 20964 Comm: bash Tainted: G I 6.0.0-rc3-foll-numa+ #41 > >>> ... > >>> RIP: 0010:split_huge_pages_write+0xcf4/0xe30 > >>> > >>> This shows that page_to_nid() in page_zone() is unexpectedly called for an > >>> offlined memmap. > >>> > >>> Use pfn_to_online_page() to get struct page in PFN walker. > >> > >> With changes proposed by David, this patch looks good to me. > >> > >> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> > > > > Thank you. > > > >> > >> BTW: IMHO, there might be many similar code places need to take care of memory hotremove where > >> *pfn is operated directly* while it's not protected against memory hotremove. > > > > I had the similar concern, but there seems many place doing PFN walk, > > so checking them one-by-one that offlined memory can be walked over > > requires much effort. > > Yes, that will be a heavy work. We could fix them one by one if they ever occur. ;) Most of those whic are directly triggerable should be taken care of. It would be still good to go through `git grep -w pfn_to_page' and evaluate all callers. Still more than 400 callsites so not a trivial task. -- Michal Hocko SUSE Labs
