Re: arm32: panic in move_freepages (Was [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid())

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2021/5/6 20:47, Kefeng Wang wrote:
> 
> 
>>>>> no, the CONFIG_ARM_LPAE is not set, and yes with same panic at
>>>>> move_freepages at
>>>>>
>>>>> start_pfn/end_pfn [de600, de7ff], [de600000, de7ff000] :  pfn 
>>>>> =de600, page
>>>>> =ef3cc000, page-flags = ffffffff,  pfn2phy = de600000
>>>>>
>>>>>>> __free_memory_core, range: 0xb0200000 - 0xc0000000, pfn: b0200 - 
>>>>>>> b0200
>>>>>>> __free_memory_core, range: 0xcc000000 - 0xdca00000, pfn: cc000 - 
>>>>>>> b0200
>>>>>>> __free_memory_core, range: 0xde700000 - 0xdea00000, pfn: de700 - 
>>>>>>> b0200
>>>>
>>>> Hmm, [de600, de7ff] is not added to the free lists which is correct. 
>>>> But
>>>> then it's unclear how the page for de600 gets to move_freepages()...
>>>>
>>>> Can't say I have any bright ideas to try here...
>>>
>>> Are we missing some checks (e.g., PageReserved()) that 
>>> pfn_valid_within()
>>> would have "caught" before?
>>
>> Unless I'm missing something the crash happens in __rmqueue_fallback():
>>
>> do_steal:
>>     page = get_page_from_free_area(area, fallback_mt);
>>
>>     steal_suitable_fallback(zone, page, alloc_flags, start_migratetype,
>>                                 can_steal);
>>         -> move_freepages()
>>             -> BUG()
>>
>> So a page from free area should be sane as the freed range was never 
>> added
>> it to the free lists.
> 
> Sorry for the late response due to the vacation.
> 
> The pfn in range [de600, de7ff] won't be added into the free lists via 
> __free_memory_core(), but the pfn could be added into freelists via 
> free_highmem_page()
> 
> I add some debug[1] in add_to_free_list(), we could see the calltrace
> 
> free_highpages, range_pfn [b0200, c0000], range_addr [b0200000, c0000000]
> free_highpages, range_pfn [cc000, dca00], range_addr [cc000000, dca00000]
> free_highpages, range_pfn [de700, dea00], range_addr [de700000, dea00000]
> add_to_free_list, ===> pfn = de700
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 0 at mm/page_alloc.c:900 add_to_free_list+0x8c/0xec
> pfn = de700
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0+ #48
> Hardware name: Hisilicon A9
> [<c010a600>] (show_stack) from [<c04b21c4>] (dump_stack+0x9c/0xc0)
> [<c04b21c4>] (dump_stack) from [<c011c708>] (__warn+0xc0/0xec)
> [<c011c708>] (__warn) from [<c011c7a8>] (warn_slowpath_fmt+0x74/0xa4)
> [<c011c7a8>] (warn_slowpath_fmt) from [<c023721c>] 
> (add_to_free_list+0x8c/0xec)
> [<c023721c>] (add_to_free_list) from [<c0237e00>] 
> (free_pcppages_bulk+0x200/0x278)
> [<c0237e00>] (free_pcppages_bulk) from [<c0238d14>] 
> (free_unref_page+0x58/0x68)
> [<c0238d14>] (free_unref_page) from [<c023bb54>] 
> (free_highmem_page+0xc/0x50)
> [<c023bb54>] (free_highmem_page) from [<c070620c>] (mem_init+0x21c/0x254)
> [<c070620c>] (mem_init) from [<c0700b38>] (start_kernel+0x258/0x5c0)
> [<c0700b38>] (start_kernel) from [<00000000>] (0x0)
> 
> so any idea?

If pfn = 0xde700, due to the pageblock_nr_pages = 0x200, then the 
start_pfn,end_pfn passed to move_freepages() will be [de600, de7ff],
but the range of [de600,de700] without ‘struct page' will lead to
this panic when pfn_valid_within not enabled if no HOLES_IN_ZONE,
and the same issue will occurred in isolate_freepages_block(), maybe
there are some scene, so I select HOLES_IN_ZONE in ARCH_HISI(ARM) to 
solve this issue in our 5.10, should we select HOLES_IN_ZONE in all ARM 
or only in ARCH_HISI, any better solution?  Thanks.