Re: ##freemail## Re: [PATCH v2] mm/hwpoison: use pr_err() instead of dump_page() in get_any_page()

[Yang Shi <shy828301@gmail.com>]

On Mon, May 9, 2022 at 12:14 AM HORIGUCHI NAOYA(堀口　直也)
<naoya.horiguchi@nec.com> wrote:
>
> On Thu, Apr 28, 2022 at 10:25:33AM -0700, Yang Shi wrote:
> > On Tue, Apr 26, 2022 at 10:32 PM Naoya Horiguchi
> > <naoya.horiguchi@linux.dev> wrote:
> > >
> > > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > >
> > > The following VM_BUG_ON_FOLIO() is triggered when memory error event
> > > happens on the (thp/folio) pages which are about to be freed:
> > >
> > >   [ 1160.232771] page:00000000b36a8a0f refcount:1 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x16a000
> > >   [ 1160.236916] page:00000000b36a8a0f refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x16a000
> > >   [ 1160.240684] flags: 0x57ffffc0800000(hwpoison|node=1|zone=2|lastcpupid=0x1fffff)
> > >   [ 1160.243458] raw: 0057ffffc0800000 dead000000000100 dead000000000122 0000000000000000
> > >   [ 1160.246268] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
> > >   [ 1160.249197] page dumped because: VM_BUG_ON_FOLIO(!folio_test_large(folio))
> > >   [ 1160.251815] ------------[ cut here ]------------
> > >   [ 1160.253438] kernel BUG at include/linux/mm.h:788!
> > >   [ 1160.256162] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> > >   [ 1160.258172] CPU: 2 PID: 115368 Comm: mceinj.sh Tainted: G            E     5.18.0-rc1-v5.18-rc1-220404-2353-005-g83111+ #3
> > >   [ 1160.262049] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35 04/01/2014
> > >   [ 1160.265103] RIP: 0010:dump_page.cold+0x27e/0x2bd
> > >   [ 1160.266757] Code: fe ff ff 48 c7 c6 81 f1 5a 98 e9 4c fe ff ff 48 c7 c6 a1 95 59 98 e9 40 fe ff ff 48 c7 c6 50 bf 5a 98 48 89 ef e8 9d 04 6d ff <0f> 0b 41 f7 c4 ff 0f 00 00 0f 85 9f fd ff ff 49 8b 04 24 a9 00 00
> > >   [ 1160.273180] RSP: 0018:ffffaa2c4d59fd18 EFLAGS: 00010292
> > >   [ 1160.274969] RAX: 000000000000003e RBX: 0000000000000001 RCX: 0000000000000000
> > >   [ 1160.277263] RDX: 0000000000000001 RSI: ffffffff985995a1 RDI: 00000000ffffffff
> > >   [ 1160.279571] RBP: ffffdc9c45a80000 R08: 0000000000000000 R09: 00000000ffffdfff
> > >   [ 1160.281794] R10: ffffaa2c4d59fb08 R11: ffffffff98940d08 R12: ffffdc9c45a80000
> > >   [ 1160.283920] R13: ffffffff985b6f94 R14: 0000000000000000 R15: ffffdc9c45a80000
> > >   [ 1160.286641] FS:  00007eff54ce1740(0000) GS:ffff99c67bd00000(0000) knlGS:0000000000000000
> > >   [ 1160.289498] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > >   [ 1160.291106] CR2: 00005628381a5f68 CR3: 0000000104712003 CR4: 0000000000170ee0
> > >   [ 1160.293031] Call Trace:
> > >   [ 1160.293724]  <TASK>
> > >   [ 1160.294334]  get_hwpoison_page+0x47d/0x570
> > >   [ 1160.295474]  memory_failure+0x106/0xaa0
> > >   [ 1160.296474]  ? security_capable+0x36/0x50
> > >   [ 1160.297524]  hard_offline_page_store+0x43/0x80
> > >   [ 1160.298684]  kernfs_fop_write_iter+0x11c/0x1b0
> > >   [ 1160.299829]  new_sync_write+0xf9/0x160
> > >   [ 1160.300810]  vfs_write+0x209/0x290
> > >   [ 1160.301835]  ksys_write+0x4f/0xc0
> > >   [ 1160.302718]  do_syscall_64+0x3b/0x90
> > >   [ 1160.303664]  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >   [ 1160.304981] RIP: 0033:0x7eff54b018b7
> > >
> > > As shown in the RIP address, this VM_BUG_ON in folio_entire_mapcount() is
> > > called from dump_page("hwpoison: unhandlable page") in get_any_page().
> > > The below explains the mechanism of the race:
> > >
> > >   CPU 0                                       CPU 1
> > >
> > >     memory_failure
> > >       get_hwpoison_page
> > >         get_any_page
> > >           dump_page
> > >             compound = PageCompound
> > >                                                 free_pages_prepare
> > >                                                   page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP
> > >             folio_entire_mapcount
> > >               VM_BUG_ON_FOLIO(!folio_test_large(folio))
> > >
> > > So replace dump_page() with safer one, pr_err().
> > >
> > > Fixes: 74e8ee4708a8 ("mm: Turn head_compound_mapcount() into folio_entire_mapcount()")
> > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > > ---
> > > ChangeLog v1 -> v2:
> > > - v1: https://lore.kernel.org/linux-mm/20220414235950.840409-1-naoya.horiguchi@linux.dev/T/#u
> > > - update caller side instead of changing dump_page().
> > > ---
> > >  mm/memory-failure.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > > index 35e11d6bea4a..0e1453514a2b 100644
> > > --- a/mm/memory-failure.c
> > > +++ b/mm/memory-failure.c
> > > @@ -1270,7 +1270,7 @@ static int get_any_page(struct page *p, unsigned long flags)
> > >         }
> > >  out:
> > >         if (ret == -EIO)
> > > -               dump_page(p, "hwpoison: unhandlable page");
> > > +               pr_err("Memory failure: %#lx: unhandlable page.\n", page_to_pfn(p));
> >
> > I think dump_page() is helpful to tell the users more information
> > about the unhandlable page, I'm ok with this fix for now, but should
> > we consider having a memory failure safe dump_page() in the future?
>
> Yes, maybe that would be helpful not only in this unhandlable case, so sounds
> good to me.  But how do we handle folio's case?  And I'm not sure that the full
> info in dump_page() is needed in a memory_failure-specific variant.

Off the top of my head, we just dump the raw information of the page
and the head page if it belongs to a large folio at the moment? This
may be just slightly different from dump_page().

>
> Thanks,
> Naoya Horiguchi