linux-kernel - Re: [PATCH v5 0/2] arm64: Fix pending single-step debugging issues

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Date:   Fri, 27 Jan 2023 11:34:36 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     will@...nel.org, catalin.marinas@....com, liwei391@...wei.com,
        mhiramat@...nel.org, maz@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, dianders@...omium.org
Subject: Re: [PATCH v5 0/2] arm64: Fix pending single-step debugging issues

On Tue, 24 Jan 2023 at 23:34, Daniel Thompson
<daniel.thompson@...aro.org> wrote:
>
> On Thu, Jan 12, 2023 at 02:52:49PM +0530, Sumit Garg wrote:
> > Hi Will, Catalin,
> >
> > On Mon, 19 Dec 2022 at 15:55, Sumit Garg <sumit.garg@...aro.org> wrote:
> > >
> > > This patch-set reworks pending fixes from Wei's series [1] to make
> > > single-step debugging via kgdb/kdb on arm64 work as expected. There was
> > > a prior discussion on ML [2] regarding if we should keep the interrupts
> > > enabled during single-stepping. So patch #1 follows suggestion from Will
> > > [3] to not disable interrupts during single stepping but rather skip
> > > single stepping within interrupt handler.
> > >
> > > [1] https://lore.kernel.org/all/20200509214159.19680-1-liwei391@huawei.com/
> > > [2] https://lore.kernel.org/all/CAD=FV=Voyfq3Qz0T3RY+aYWYJ0utdH=P_AweB=13rcV8GDBeyQ@mail.gmail.com/
> > > [3] https://lore.kernel.org/all/20200626095551.GA9312@willie-the-truck/
> > >
> > > Changes in v5:
> > > - Incorporated misc. comments from Mark.
> > >
> >
> > Since patch #1 has already been reviewed/acked by Mark and the
> > complete patchset has been tested by Doug, would it be fine for you to
> > pick up this patchset? It fixes a real single stepping problem for
> > kgdb on arm64.
>
> Sorry to be quiet for so long.
>
> Testing this patch set has proven to be a little difficult.
>
> It certainly fixes the single step tests in the kgdbtest suite.
> That's a good start.
>
> Unfortunately when testing using qemu/KVM (hosted on NXP
> 2k/Solidrun Honeycomb) the patch set is resulting in instability
> running the built-in self tests (specifically this one:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/misc/kgdbts.c#n74 ). Running this test using the kgdbtest harness
> results in the test failing roughly a third of the time.
>
> The error reported is that the trap handler tried to unlock a spinlock
> that isn't currently locked. To be honest I suspect this is a generic
> problem that the new feature happens to tickle (this test has
> historically been unreliable on x86 too... and x86 is noteworthy for
> being the only other platform I test using KVM rather than pure qemu).
> Of course the only way to prove that would be to find and fix the
> problem in the trap handler (which probably involves rewriting it) and I
> haven't managed to do that yet.
>
> In short, I think the debugger is more useful with this patchset than
> without so, although it is caveated by the above, I'd call this:
>
> Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
> Tested-by: Daniel Thompson <daniel.thompson@...aro.org>
>

Thanks Daniel for the in-depth testing.

-Sumit

>
> Daniel.