linux-kernel - Re: [Update] Regression in 4.18 - 32-bit PowerPC crashes on boot

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Date:   Fri, 29 Jun 2018 19:55:30 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Pekka Enberg <penberg@...nel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Christoph Lameter <cl@...ux.com>,
        ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [Update] Regression in 4.18 - 32-bit PowerPC crashes on boot - bisected to commit 1d40a5ea01d5

On Fri, Jun 29, 2018 at 02:01:46PM -0700, Linus Torvalds wrote:
> On Fri, Jun 29, 2018 at 1:42 PM Larry Finger <Larry.Finger@...inger.net> wrote:
> But the real question is what the problem was the *first* time around.
> I assume that has scrolled off the screen? This part:
> 
>   _exception_pkey+0x58/0x128
>   ret_from_except_full+0x0/0x4
>   --- interrupt: 700 at free_pgd_range+0x19c/0x30c
>        LR = free_pgd_range+0x19c/0x30c
>   free_pgtables+0xa/0xb
>   exit_mnap+0xf4/0x16c
>   mmput+0x64/0xf0
> 
> Does reverting that commit 1d40a5ea01d5 make everything work for you?
> Because if so, judging by the deafening silence on this so far, I
> think that's what we should do.
> 
> That said, can some ppc person who knows the 32-bit ppc code and maybe
> knows what that "interrupt: 700" means talk about that oddity in the
> trace, please?

700 is "program interrupt"; here it probably means a BUG() happened (which
does a trap instruction, which causes a 700).  The stuff that scrolled away
should tell more.


Segher