linux-kernel - Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si

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Date:   Wed, 21 Apr 2021 09:35:22 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian@...uner.io>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Matt Morehouse <mascasa@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and
 si_perf to siginfo

On 21.04.2021 08:21, Marek Szyprowski wrote:
> On 21.04.2021 00:42, Marco Elver wrote:
>> On Tue, 20 Apr 2021 at 23:26, Marek Szyprowski 
>> <m.szyprowski@...sung.com> wrote:
>>> On 08.04.2021 12:36, Marco Elver wrote:
>>>> Introduces the TRAP_PERF si_code, and associated siginfo_t field
>>>> si_perf. These will be used by the perf event subsystem to send 
>>>> signals
>>>> (if requested) to the task where an event occurred.
>>>>
>>>> Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org> # m68k
>>>> Acked-by: Arnd Bergmann <arnd@...db.de> # asm-generic
>>>> Signed-off-by: Marco Elver <elver@...gle.com>
>>> This patch landed in linux-next as commit fb6cc127e0b6 ("signal:
>>> Introduce TRAP_PERF si_code and si_perf to siginfo"). It causes
>>> regression on my test systems (arm 32bit and 64bit). Most systems fails
>>> to boot in the given time frame. I've observed that there is a timeout
>>> waiting for udev to populate /dev and then also during the network
>>> interfaces configuration. Reverting this commit, together with
>>> 97ba62b27867 ("perf: Add support for SIGTRAP on perf events") to let it
>>> compile, on top of next-20210420 fixes the issue.
>> Thanks, this is weird for sure and nothing in particular stands out.
>>
>> I have questions:
>> -- Can you please share your config?
>
> This happens with standard multi_v7_defconfig (arm) or just defconfig 
> for arm64.
>
>> -- Also, can you share how you run this? Can it be reproduced in qemu?
> Nothing special. I just boot my test systems and see that they are 
> waiting lots of time during the udev populating /dev and network 
> interfaces configuration. I didn't try with qemu yet.
>> -- How did you derive this patch to be at fault? Why not just
>> 97ba62b27867, given you also need to revert it?
> Well, I've just run my boot tests with automated 'git bisect' and that 
> was its result. It was a bit late in the evening, so I didn't analyze 
> it further, I've just posted a report about the issue I've found. It 
> looks that bisecting pointed to a wrong commit somehow.
>> If you are unsure which patch exactly it is, can you try just
>> reverting 97ba62b27867 and see what happens?
>
> Indeed, this is a real faulty commit. Initially I've decided to revert 
> it to let kernel compile (it uses some symbols introduced by this 
> commit). Reverting only it on top of linux-next 20210420 also fixes 
> the issue. I'm sorry for the noise in this thread. I hope we will find 
> what really causes the issue.

This was a premature conclusion. It looks that during the test I've did 
while writing that reply, the modules were not deployed properly and a 
test board (RPi4) booted without modules. In that case the board booted 
fine and there was no udev timeout. After deploying kernel modules, the 
udev timeout is back.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland