linux-kernel - Re: [PATCH 1/5] MIPS: kdb: Remove old workaround for backtracing on other CPUs

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Message-ID: <20191115003051.blbbwr7hmuqyzjwb@lantea.localdomain>
Date:   Thu, 14 Nov 2019 16:30:51 -0800
From:   Paul Burton <paulburton@...nel.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Paul Burton <paul.burton@...s.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        qiaochong@...ngson.cn, kgdb-bugreport@...ts.sourceforge.net,
        ralf@...ux-mips.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        James Hogan <jhogan@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        Philippe Mathieu-Daudé <f4bug@...at.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/5] MIPS: kdb: Remove old workaround for backtracing on
 other CPUs

Hi Daniel,

On Thu, Nov 14, 2019 at 10:51:25AM +0000, Daniel Thompson wrote:
> On Sat, Nov 09, 2019 at 11:16:40AM -0800, Douglas Anderson wrote:
> > As of commit 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs
> > that aren't the master") we no longer need any special case for doing
> > stack dumps on CPUs that are not the kdb master.  Let's remove.
> > 
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> > I have no way to test this personally, so hopefully someone who uses
> > kdb/kgdb on MIPS can.
> 
> I took this as a hint to add mips support to kgdbtest ;-)

Wonderful! :)

> Support is added and working well. Unfortunately lack of familiarity
> with mips means I have not yet figured out which mips defconfig gives
> us working SMP (and what the corresponding qemu invocation should be).

You can build 64r6el_defconfig & boot it something like this:

$ qemu-system-mips64el \
    -M boston -cpu I6500 -smp 4 \
    -kernel arch/mips/boot/vmlinux.gz.itb \
    -serial stdio \
    -hda my-disk-image.bin \
    -append "root=/dev/sda"

Linux should see the system as a single core with 4 hardware threads
(VPs or Virtual Processors in MIPS terminology).

> > Ideally this patch should be Acked by MIPS folks and then land through
> > the kdb/kgdb tree since the next patch in the series, ("kdb:
> > kdb_current_regs should be private") depends on it.
> 
> An Acked-by from a MIPS maintainer would be very welcome. Perhaps
> with a bit of extra work on the above I might be able to provide
> a Tested-by:.

The patches look reasonable to me; I was hoping to test them before
giving an ack but haven't had the time yet. It seems you may be making
that easier :)

Thanks,
    Paul