linux-kernel - Re: [next] arm: Internal error: Oops: 5 PC is at __read_once_word

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Date:   Wed, 9 Mar 2022 17:47:42 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        open list <linux-kernel@...r.kernel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [next] arm: Internal error: Oops: 5 PC is at __read_once_word_nocheck

On Wed, 9 Mar 2022 at 17:38, Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>
> Hi Russell,
>
> On Wed, 9 Mar 2022 at 20:37, Russell King (Oracle)
> <linux@...linux.org.uk> wrote:
> >
> > On Wed, Mar 09, 2022 at 03:57:32PM +0100, Ard Biesheuvel wrote:
> > > On Wed, 9 Mar 2022 at 15:44, Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
> > > >
> <trim>
> > Well, we unwound until:
> >
> >  __irq_svc from migrate_disable+0x0/0x70
> >
> > and then crashed - and the key thing there is that we're at the start
> > of migrate_disable() when we took an interrupt.
> >
> > For some reason, this triggers an access to address 0x10, which faults.
> > We then try unwinding again, and successfully unwind all the way back
> > to the same point (the line above) which then causes the unwinder to
> > again access address 0x10, and the cycle repeats with the stack
> > growing bigger and bigger.
> >
> > I'd suggest also testing without the revert but with my patch.
>
> I have tested your patch on top of linux next-20220309 and still see kernel
> crash as below [1]. build link [2].
>
> [   26.812060] 8<--- cut here ---
> [   26.813459] Unhandled fault: page domain fault (0x01b) at 0xb6a3ab70
> [   26.816139] [b6a3ab70] *pgd=fb28a835
> [   26.817770] Internal error: : 1b [#1] SMP ARM
> [   26.819636] Modules linked in:
> [   26.820956] CPU: 0 PID: 211 Comm: haveged Not tainted
> 5.17.0-rc7-next-20220309 #1
> [   26.824519] Hardware name: Generic DT based system
> [   26.827148] PC is at __read_once_word_nocheck+0x0/0x8
> [   26.829856] LR is at unwind_frame+0x7dc/0xab4
>

Thanks Naresh,

Is this something that could be bisected? With the unwind change
reverted, it is not obvious where the problem originated. Also, could
you check whether it is reproducible on the ARM tree? (for-next on
git://git.armlinux.org.uk/~rmk/linux-arm.git)

Unfortunately, after having been able to reproduce this locally, the
issue went away when I did the revert, so I am no longer seeing the
problem.

-- 
Ard.