Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si_perf to siginfo

From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexander Potapenko <glider@google.com>,
	Al Viro <viro@zeniv.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>,
	Christian Brauner <christian@brauner.io>,
	Dmitry Vyukov <dvyukov@google.com>, Jann Horn <jannh@google.com>,
	Jens Axboe <axboe@kernel.dk>, Matt Morehouse <mascasa@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Ian Rogers <irogers@google.com>, Oleg Nesterov <oleg@redhat.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si_perf to siginfo
Date: Wed, 21 Apr 2021 08:21:17 +0200	[thread overview]
Message-ID: <43f8a3bf-34c5-0fc9-c335-7f92eaf23022@samsung.com> (raw)
In-Reply-To: <CANpmjNM8wEJngK=J8Lt9npkZgrSWoRsqkdajErWEoY_=M1GW5A@mail.gmail.com>

Hi,

On 21.04.2021 00:42, Marco Elver wrote:
> On Tue, 20 Apr 2021 at 23:26, Marek Szyprowski <m.szyprowski@samsung.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@linux-m68k.org> # m68k
>>> Acked-by: Arnd Bergmann <arnd@arndb.de> # asm-generic
>>> Signed-off-by: Marco Elver <elver@google.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.

Best regards

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