linux-kernel - Re: [PATCH v2 0/3] arm64: Convert to ARCH

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Date:   Wed, 2 Sep 2020 20:03:06 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH v2 0/3] arm64: Convert to ARCH_STACKWALK

On Wed, Sep 02, 2020 at 06:38:03PM +0100, Mark Brown wrote:
> On Tue, Sep 01, 2020 at 05:06:26PM +0100, Mark Rutland wrote:
> 
> > Just to check, has the skipping logic been tested to work equivalently
> > to what we had before? By inspection I think it should, but since it
> > relies on function call boundaries it always strikes me as fragile.
> 
> > If you could confirm that (e.g. with LKDTM perhaps?) that'd be great.
> > Assuming that looks right, for the series:
> 
> I've tested this with LKDTM and otherwise and didn't spot any issues
> (and just did a bit of retesting) but it is a pretty manual process so
> it's possible I missed something.

It looks like the case Mirolav pointed out (self-bactrace with NULL
regs) isn't triggered by LKDTM (since it always causes a backtrace from
an exception with non-NULL regs), but we do rely on that elsewhere in
the kernel.

It might be worth adding an LKDTM test to trigger that.

I'll wait for a respin that handles that -- please drop the ack for now.

Thanks,
Mark.