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

[Kefeng Wang]

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.