Re: [PATCH] mm/memory-failure.c: bail out early if huge zero page

[Yu Xu <xuyu@linux.alibaba.com>]

On 4/12/22 5:09 PM, Naoya Horiguchi wrote:
> On Mon, Apr 11, 2022 at 10:18:26AM +0800, Miaohe Lin wrote:
>> On 2022/4/10 23:22, Xu Yu wrote:
>>> Kernel panic when injecting memory_failure for the global huge_zero_page,
>>> when CONFIG_DEBUG_VM is enabled, as follows.
>>>
>>> [    5.582720] Injecting memory failure for pfn 0x109ff9 at process virtual address 0x20ff9000
>>> [    5.583786] page:00000000fb053fc3 refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x109e00
>>> [    5.584900] head:00000000fb053fc3 order:9 compound_mapcount:0 compound_pincount:0
>>> [    5.585796] flags: 0x17fffc000010001(locked|head|node=0|zone=2|lastcpupid=0x1ffff)
>>> [    5.586712] raw: 017fffc000010001 0000000000000000 dead000000000122 0000000000000000
>>> [    5.587640] raw: 0000000000000000 0000000000000000 00000002ffffffff 0000000000000000
>>> [    5.588565] page dumped because: VM_BUG_ON_PAGE(is_huge_zero_page(head))
>>> [    5.589398] ------------[ cut here ]------------
>>> [    5.589952] kernel BUG at mm/huge_memory.c:2499!
>>> [    5.590516] invalid opcode: 0000 [#1] PREEMPT SMP PTI
>>> [    5.591120] CPU: 6 PID: 553 Comm: split_bug Not tainted 5.18.0-rc1+ #11
>>> [    5.591904] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 3288b3c 04/01/2014
>>> [    5.592817] RIP: 0010:split_huge_page_to_list+0x66a/0x880
>>> [    5.593469] Code: 84 9b fb ff ff 48 8b 7c 24 08 31 f6 e8 9f 5d 2a 00 b8 b8 02 00 00 e9 e8 fb ff ff 48 c7 c6 e8 47 3c 82 4c b
>>> [    5.595806] RSP: 0018:ffffc90000dcbdf8 EFLAGS: 00010246
>>> [    5.596434] RAX: 000000000000003c RBX: 0000000000000001 RCX: 0000000000000000
>>> [    5.597322] RDX: 0000000000000000 RSI: ffffffff823e4c4f RDI: 00000000ffffffff
>>> [    5.598162] RBP: ffff88843fffdb40 R08: 0000000000000000 R09: 00000000fffeffff
>>> [    5.598999] R10: ffffc90000dcbc48 R11: ffffffff82d68448 R12: ffffea0004278000
>>> [    5.599849] R13: ffffffff823c6203 R14: 0000000000109ff9 R15: ffffea000427fe40
>>> [    5.600693] FS:  00007fc375a26740(0000) GS:ffff88842fd80000(0000) knlGS:0000000000000000
>>> [    5.601640] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [    5.602304] CR2: 00007fc3757c9290 CR3: 0000000102174006 CR4: 00000000003706e0
>>> [    5.603139] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> [    5.603977] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> [    5.604806] Call Trace:
>>> [    5.605101]  <TASK>
>>> [    5.605357]  ? __irq_work_queue_local+0x39/0x70
>>> [    5.605904]  try_to_split_thp_page+0x3a/0x130
>>> [    5.606430]  memory_failure+0x128/0x800
>>> [    5.606888]  madvise_inject_error.cold+0x8b/0xa1
>>> [    5.607444]  __x64_sys_madvise+0x54/0x60
>>> [    5.607915]  do_syscall_64+0x35/0x80
>>> [    5.608347]  entry_SYSCALL_64_after_hwframe+0x44/0xae
>>> [    5.608949] RIP: 0033:0x7fc3754f8bf9
>>> [    5.609374] Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 8
>>> [    5.611554] RSP: 002b:00007ffeda93a1d8 EFLAGS: 00000217 ORIG_RAX: 000000000000001c
>>> [    5.612441] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fc3754f8bf9
>>> [    5.613269] RDX: 0000000000000064 RSI: 0000000000003000 RDI: 0000000020ff9000
>>> [    5.614108] RBP: 00007ffeda93a200 R08: 0000000000000000 R09: 0000000000000000
>>> [    5.614946] R10: 00000000ffffffff R11: 0000000000000217 R12: 0000000000400490
>>> [    5.615787] R13: 00007ffeda93a2e0 R14: 0000000000000000 R15: 0000000000000000
>>> [    5.616626]  </TASK>
>>>
>>
>> Thanks for the report and the patch!
>>
>> I remember I and Naoya discussed the try_to_split_thp_page in memory_failure might come
>> across non-lru movable compound page and huge_zero_page. We fixed the non-lru movable
>> compound page case but conclude huge_zero_page won't reach here due to the HWPoisonHandlable()
>> check. But we missed the MF_COUNT_INCREASED case where HWPoisonHandlable() is skipped.
>>
>>> In fact, huge_zero_page is unhandlable currently in either soft offline
>>> or memory failure injection.  With CONFIG_DEBUG_VM disabled,
>>> huge_zero_page is bailed out when checking HWPoisonHandlable() in
>>> get_any_page(), or checking page mapping in split_huge_page_to_list().
>>>
>>> This makes huge_zero_page bail out early in madvise_inject_error(), and
>>> panic above won't happen again.
>>
>> It seems this issue is expected to happen only in madvise_inject_error case because
>> MF_COUNT_INCREASED is only set here. So this fix should do the right thing. But I
>> don't know whether bail out early for huge_zero_page is suitable.
>>
>> Hi Naoya, what do you think?
> 
> Thank you for reporting.
> 
> ...
> 
>>> @@ -1087,12 +1087,21 @@ static int madvise_inject_error(int behavior,
>>>   			return ret;
>>>   		pfn = page_to_pfn(page);
>>>   
>>> +		head = compound_head(page);
>>> +		if (unlikely(is_huge_zero_page(head))) {
>>> +			pr_warn("Unhandlable attempt to %s pfn %#lx at process virtual address %#lx\n",
>>> +				behavior == MADV_SOFT_OFFLINE ? "soft offline" :
>>> +								"inject memory failure for",
>>> +				pfn, start);
>>> +			return -EINVAL;
>>> +		}
> 
> This check is about the detail of error handling, so I feel it desirable to
> do this in memory_failure().  And memory errors on huge zero page is the
> real scenario, so it seems to me better to make this case injectable rather
> than EINVAL.
> 
> How about checking is_huge_zero_page() before try_to_split_thp_page()?
> The result should be consistent with the results when called by other
> memory_failure()'s callers  like MCE handler and hard_offline_page_store().

Agree. thanks!

> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 9b76222ee237..771fb4fc626c 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1852,6 +1852,12 @@ int memory_failure(unsigned long pfn, int flags)
>   	}
>   
>   	if (PageTransHuge(hpage)) {
> +		if (is_huge_zero_page(hpage)) {
> +			action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);

Should we use MF_MSG_UNSPLIT_THP instead of MF_MSG_KERNEL_HIGH_ORDER?

And should we SetPageHasHWPoisoned(hpage) for huge zero page, since
TestSetPageHWPoison(p) is done in the early part of memory_failure().

> +			res = -EBUSY;
> +			goto unlock_mutex;
> +		}
> +
>   		/*
>   		 * The flag must be set after the refcount is bumped
>   		 * otherwise it may race with THP split.
> 
> 
> Thanks,
> Naoya Horiguchi

-- 
Thanks,
Yu