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. Thanks, Naoya Horiguchi
