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From: Yang Shi <shy828301@gmail.com>
Date: Wed, 15 May 2024 09:58:32 -0600
Message-ID: <CAHbLzkrO9-yWRFrWoE0idWwMffkBWNSku6iO2vdPLCpWAY7wQg@mail.gmail.com>
Subject: Re: [PATCH v2] mm/huge_memory: don't unpoison huge_zero_folio
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: akpm@linux-foundation.org, nao.horiguchi@gmail.com, xuyu@linux.alibaba.com, 
	david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Tue, May 14, 2024 at 8:39=E2=80=AFPM Miaohe Lin <linmiaohe@huawei.com> w=
rote:
>
> When I did memory failure tests recently, below panic occurs:
>
>  kernel BUG at include/linux/mm.h:1135!
>  invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
>  CPU: 9 PID: 137 Comm: kswapd1 Not tainted 6.9.0-rc4-00491-gd5ce28f156fe-=
dirty #14
>  RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
>  RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
>  RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
>  RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
>  RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
>  R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
>  R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
>  FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:000000000000=
0000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0
>  Call Trace:
>   <TASK>
>   do_shrink_slab+0x14f/0x6a0
>   shrink_slab+0xca/0x8c0
>   shrink_node+0x2d0/0x7d0
>   balance_pgdat+0x33a/0x720
>   kswapd+0x1f3/0x410
>   kthread+0xd5/0x100
>   ret_from_fork+0x2f/0x50
>   ret_from_fork_asm+0x1a/0x30
>   </TASK>
>  Modules linked in: mce_inject hwpoison_inject
>  ---[ end trace 0000000000000000 ]---
>  RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
>  RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
>  RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
>  RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
>  RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
>  R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
>  R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
>  FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:000000000000=
0000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0
>
> The root cause is that HWPoison flag will be set for huge_zero_folio
> without increasing the folio refcnt. But then unpoison_memory() will
> decrease the folio refcnt unexpectly as it appears like a successfully
> hwpoisoned folio leading to VM_BUG_ON_PAGE(page_ref_count(page) =3D=3D 0)
> when releasing huge_zero_folio.
>
> Skip unpoisoning huge_zero_folio in unpoison_memory() to fix this issue.
> We're not prepared to unpoison huge_zero_folio yet.
>
> Fixes: 478d134e9506 ("mm/huge_memory: do not overkill when splitting huge=
_zero_page")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> Cc: <stable@vger.kernel.org>

Reviewed-by: Yang Shi <shy828301@gmail.com>

> ---
> v2:
>  Change to simply check for the huge zero page. Thanks.
> ---
>  mm/memory-failure.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 16ada4fb02b7..68bc8d7ff53d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2558,6 +2558,12 @@ int unpoison_memory(unsigned long pfn)
>                 goto unlock_mutex;
>         }
>
> +       if (is_huge_zero_folio(folio)) {
> +               unpoison_pr_info("Unpoison: huge zero page is not support=
ed %#lx\n",
> +                                pfn, &unpoison_rs);
> +               goto unlock_mutex;
> +       }
> +
>         if (folio_test_slab(folio) || folio_test_pgtable(folio) ||
>             folio_test_reserved(folio) || folio_test_offline(folio))
>                 goto unlock_mutex;
> --
> 2.33.0
>