linux-kernel - Re: [REPOST PATCH v6 0/4] kgdb: Fix kgdb_roundup

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Message-ID: <20181210135038.GC4048@arrakis.emea.arm.com>
Date:   Mon, 10 Dec 2018 13:50:39 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     mhocko@...e.com, Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-sh@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Will Deacon <will.deacon@....com>,
        LKML <linux-kernel@...r.kernel.org>, dalias@...c.org,
        paulus@...ba.org, mpe@...erman.id.au,
        "H. Peter Anvin" <hpa@...or.com>, sparclinux@...r.kernel.org,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-hexagon@...r.kernel.org, x86@...nel.org,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>, ying.huang@...el.com,
        jhogan@...nel.org, linux-snps-arc@...ts.infradead.org,
        rppt@...ux.vnet.ibm.com, bp@...en8.de,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        christophe.leroy@....fr, Vineet Gupta <vgupta@...opsys.com>,
        linux-mips@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        rkuo@...eaurora.org, paul.burton@...s.com,
        Jason Wessel <jason.wessel@...driver.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [REPOST PATCH v6 0/4] kgdb: Fix kgdb_roundup_cpus()

Hi Doug,

On Fri, Dec 07, 2018 at 10:40:24AM -0800, Doug Anderson wrote:
> On Fri, Dec 7, 2018 at 9:42 AM Catalin Marinas <catalin.marinas@....com> wrote:
> > On Tue, Dec 04, 2018 at 07:38:24PM -0800, Douglas Anderson wrote:
> > > Douglas Anderson (4):
> > >   kgdb: Remove irq flags from roundup
> > >   kgdb: Fix kgdb_roundup_cpus() for arches who used smp_call_function()
> > >   kgdb: Don't round up a CPU that failed rounding up before
> > >   kdb: Don't back trace on a cpu that didn't round up
> >
> > FWIW, trying these on arm64 (ThunderX2) with CONFIG_KGDB_TESTS_ON_BOOT=y
> > on top of 4.20-rc5 doesn't boot. It looks like they leave interrupts
> > disabled when they shouldn't and it trips over the BUG at
> > mm/vmalloc.c:1380 (called via do_fork -> copy_process).
> >
> > Now, I don't think these patches make things worse on arm64 since prior
> > to them the kgdb boot tests on arm64 were stuck in a loop (RUN
> > singlestep).
> 
> Thanks for the report!  ...actually, I'd never tried CONFIG_KGDB_TESTS
> before.  ...so I tried them now:
> 
> A) chromeos-4.19 tree on qcom-sdm845 without this series: booted up OK
> B) chromeos-4.19 tree on qcom-sdm845 with this series: booted up OK
> C) v4.20-rc5-90-g30002dd008ed on rockchip-rk3399 (kevin) with this
> series: booted up OK
> 
> Example output from B) above:
> 
> localhost ~ # dmesg | grep kgdbts
> [    2.139814] KGDB: Registered I/O driver kgdbts
> [    2.144582] kgdbts:RUN plant and detach test
> [    2.165333] kgdbts:RUN sw breakpoint test
> [    2.172990] kgdbts:RUN bad memory access test
> [    2.178640] kgdbts:RUN singlestep test 1000 iterations
> [    2.187765] kgdbts:RUN singlestep [0/1000]
> [    2.559596] kgdbts:RUN singlestep [100/1000]
> [    2.931419] kgdbts:RUN singlestep [200/1000]
> [    3.303474] kgdbts:RUN singlestep [300/1000]
> [    3.675121] kgdbts:RUN singlestep [400/1000]
> [    4.046867] kgdbts:RUN singlestep [500/1000]
> [    4.418920] kgdbts:RUN singlestep [600/1000]
> [    4.790824] kgdbts:RUN singlestep [700/1000]
> [    5.162479] kgdbts:RUN singlestep [800/1000]
> [    5.534103] kgdbts:RUN singlestep [900/1000]
> [    5.902299] kgdbts:RUN do_fork for 100 breakpoints
> [    8.463900] KGDB: Unregistered I/O driver kgdbts, debugger disabled
> 
> ...so I guess I'm a little confused.  Either I have a different config
> than you do or something is special about your machine?

I tried it now on a Juno board both as a host and a guest and boots
fine. It must be something that only triggers ThunderX2. Ignore the
report for now, if I find anything interesting I'll let you know.

-- 
Catalin