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Date:   Thu, 13 Dec 2018 15:12:09 +0000
From:   Wei Yang <richard.weiyang@gmail.com>
To:     Zaslonko Mikhail <zaslonko@linux.bm.com>
Cc:     Wei Yang <richard.weiyang@gmail.com>,
        Mikhail Zaslonko <zaslonko@linux.ibm.com>,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, mhocko@kernel.org,
        Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com
Subject: Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for
 the full memory section
Message-ID: <20181213151209.hmrhrr5gvb256bzm@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
References: <20181212172712.34019-1-zaslonko@linux.ibm.com>
 <20181212172712.34019-2-zaslonko@linux.ibm.com>
 <20181213034615.4ntpo4cl2oo5mcx4@master>
 <e4cebbae-3fcb-f03c-3d0e-a1a44ff0675a@linux.bm.com>
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On Thu, Dec 13, 2018 at 01:37:16PM +0100, Zaslonko Mikhail wrote:
>On 13.12.2018 04:46, Wei Yang wrote:
>> On Wed, Dec 12, 2018 at 06:27:12PM +0100, Mikhail Zaslonko wrote:
>>> If memory end is not aligned with the sparse memory section boundary, the
>>> mapping of such a section is only partly initialized. This may lead to
>>> VM_BUG_ON due to uninitialized struct page access from
>>> is_mem_section_removable() or test_pages_in_a_zone() function triggered by
>>> memory_hotplug sysfs handlers:
>>>
>>> Here are the the panic examples:
>>> CONFIG_DEBUG_VM=y
>>> CONFIG_DEBUG_VM_PGFLAGS=y
>>>
>>> kernel parameter mem=2050M
>>> --------------------------
>>> page:000003d082008000 is uninitialized and poisoned
>>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>>> Call Trace:
>>> ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160)
>>>  [<00000000008f15c4>] show_valid_zones+0x5c/0x190
>>>  [<00000000008cf9c4>] dev_attr_show+0x34/0x70
>>>  [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
>>>  [<00000000003e4194>] seq_read+0x204/0x480
>>>  [<00000000003b53ea>] __vfs_read+0x32/0x178
>>>  [<00000000003b55b2>] vfs_read+0x82/0x138
>>>  [<00000000003b5be2>] ksys_read+0x5a/0xb0
>>>  [<0000000000b86ba0>] system_call+0xdc/0x2d8
>>> Last Breaking-Event-Address:
>>>  [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160
>>> Kernel panic - not syncing: Fatal exception: panic_on_oops
>>>
>>> kernel parameter mem=3075M
>>> --------------------------
>>> page:000003d08300c000 is uninitialized and poisoned
>>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>>> Call Trace:
>>> ([<000000000038596c>] is_mem_section_removable+0xb4/0x190)
>>>  [<00000000008f12fa>] show_mem_removable+0x9a/0xd8
>>>  [<00000000008cf9c4>] dev_attr_show+0x34/0x70
>>>  [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
>>>  [<00000000003e4194>] seq_read+0x204/0x480
>>>  [<00000000003b53ea>] __vfs_read+0x32/0x178
>>>  [<00000000003b55b2>] vfs_read+0x82/0x138
>>>  [<00000000003b5be2>] ksys_read+0x5a/0xb0
>>>  [<0000000000b86ba0>] system_call+0xdc/0x2d8
>>> Last Breaking-Event-Address:
>>>  [<000000000038596c>] is_mem_section_removable+0xb4/0x190
>>> Kernel panic - not syncing: Fatal exception: panic_on_oops
>>>
>>> Fix the problem by initializing the last memory section of each zone
>>> in memmap_init_zone() till the very end, even if it goes beyond the zone
>>> end.
>>>
>>> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
>>> Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
>>> Cc: <stable@vger.kernel.org>
>>> ---
>>> mm/page_alloc.c | 12 ++++++++++++
>>> 1 file changed, 12 insertions(+)
>>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 2ec9cc407216..e2afdb2dc2c5 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5542,6 +5542,18 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>>> 			cond_resched();
>>> 		}
>>> 	}
>>> +#ifdef CONFIG_SPARSEMEM
>>> +	/*
>>> +	 * If the zone does not span the rest of the section then
>>> +	 * we should at least initialize those pages. Otherwise we
>>> +	 * could blow up on a poisoned page in some paths which depend
>>> +	 * on full sections being initialized (e.g. memory hotplug).
>>> +	 */
>>> +	while (end_pfn % PAGES_PER_SECTION) {
>>> +		__init_single_page(pfn_to_page(end_pfn), end_pfn, zone, nid);
>>> +		end_pfn++;
>>> +	}
>>> +#endif
>>> }
>> 
>> What will happen if the end_pfn is PAGES_PER_SECTION aligned, but there
>> is invalid pfn? For example, the page is skipped in the for loop of
>> memmap_init_zone()?
>> 
>
>If the end_pfn is PAGES_PER_SECTION aligned, we do not do any extra 
>initialization.
>If the page is skipped in the loop, it will remain uninitialized for 
>the reason (e.g. a memory hole). The behavior has not been changed here.
>

I may not describe my question clearly.

If the page is skipped, then it is uninitialized. Then would this page
trigger the call trace when read the removable sysfs?

>>>
>>> #ifdef CONFIG_ZONE_DEVICE
>>> -- 
>>> 2.16.4
>> 

-- 
Wei Yang
Help you, Help me