Re: [syzbot] WARNING in folio_lruvec_lock_irqsave

From: Roman Gushchin
Date: Wed Jun 22 2022 - 23:03:19 EST


On Thu, Jun 23, 2022 at 10:32:32AM +0800, Muchun Song wrote:
> On Wed, Jun 22, 2022 at 11:33:48PM +0800, Muchun Song wrote:
> > On Wed, Jun 22, 2022 at 06:49:31AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: ac0ba5454ca8 Add linux-next specific files for 20220622
> > > git tree: linux-next
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=14354c18080000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=12809dacb9e7c5e0
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=ec972d37869318fc3ffb
> > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+ec972d37869318fc3ffb@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > folio_put include/linux/mm.h:1227 [inline]
> > > put_page+0x217/0x280 include/linux/mm.h:1279
> > > unmap_and_move_huge_page mm/migrate.c:1343 [inline]
> > > migrate_pages+0x3dc3/0x5a10 mm/migrate.c:1440
> > > do_mbind mm/mempolicy.c:1332 [inline]
> > > kernel_mbind+0x4d7/0x7d0 mm/mempolicy.c:1479
> > > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > > entry_SYSCALL_64_after_hwframe+0x46/0xb0
> > > page has been migrated, last migrate reason: mempolicy_mbind
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 1 PID: 18925 at include/linux/memcontrol.h:800 folio_lruvec include/linux/memcontrol.h:800 [inline]
> >
> > The warning here is "VM_WARN_ON_ONCE_FOLIO(!memcg && !mem_cgroup_disabled(), folio)",
> > the memcg returned by folio_memcg() seems to be NULL which has 2 possibility, one is
> > that objcg returned by folio_objcg() is NULL, another is that obj_cgroup_memcg(objcg)
> > returns NULL. However, obj_cgroup_memcg() always returns a valid memcg. So Most likely
> > objcg is NULL meaning this page is not charged to memcg. Is this possible for LRU pages?
> >
> > I am not sure if this issue is caused by my commit cca700a8e695 ("mm: lru: use lruvec
>
> I have asked Andrew to drop this individual commit (to reduce potential impact) since
> this commit can be treated as a separate optimization patch compared to LRU page
> reparenting work. I will resend this patch again after LRU page reparenting work
> stabilizes.

Sorry, I haven't noticed this e-mail and suggested the same.
Sounds like a good idea to me.