Re: [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 Ã 22:42, Larry Finger a ÃcritÂ:
> > 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
> > ÂÂÂÂ 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