[Update] Regression in 4.18 - 32-bit PowerPC crashes on boot - bisected to commit 1d40a5ea01d5

[Larry Finger]

On 06/30/2018 04:31 AM, christophe leroy wrote:
> 
> 
> Le 29/06/2018 à 22:42, Larry Finger a écrit :
>> My PowerBook G4 Aluminum crashes on boot with 4.18-rcX kernels with a kernel 
>> BUG at include/linux/page-flags.h:700! The problem was bisected to commit 
>> 1d40a5ea01d5 ("mm: mark pages in use for page tables"). It is not possible to 
>> capture the bug with anything other than a camera. The first few lines of the 
>> traceback are as follows:
>>
>> free_pgd_range+0x19c/0x30c (unreliable)
>> free_pgtables_0xa0/0xb0
>> exit_pmap+0xf4/0x16c
>> mmput+0x64/0xf0
>> do_exit+0x33c/0x89c
>> oops_end+0x13c/0x144
>> _exception_pkey+0x58/0x128
>> ret_from_except_full+0x0/0x4
>> --- interrupt: 700 at free_pgd_range+0x19c/0x30c
>> Â Â Â Â  LR = free_pgd_range+0x19c/0x30c
>> free_pgtables+0xa/0xb
>> exit_mnap+0xf4/0x16c
>> mmput+0x64/0xf0
>> flush_old_exec+0x490/0x550
>>
>> I have more information regarding this BUG. Line 700 of page-flags.h is the 
>> macro PAGE_TYPE_OPS(Table, table). For further debugging, I manually expanded 
>> the macro, and found that the bug line is VM_BUG_ON_PAGE(!PageTable(page), 
>> page) in routine __ClearPageTable(), which is called from pgtable_page_dtor() 
>> in include/linux/mm.h. I also added a printk call to PageTable() that logs 
>> page->page_type. The routine was called twice. The first had page_type of 
>> 0xfffffbff, which would have been expected for a . The second call had 
>> 0xffffffff, which led to the BUG.
>>
> 
> Oh, seems to be the one I noticed and told Aneesh about 
> (https://patchwork.ozlabs.org/patch/922771/)
> 
> Aneesh provided the patch https://patchwork.ozlabs.org/patch/934111/ for it, 
> does it help ?

Yes, those changes fix the problem.

Larry