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Date:   Fri, 28 Oct 2022 12:59:54 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH] selftests/ftrace: Limit number of lines processed in
 'trace'
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Akanksha J N <akanksha@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        Shuah Khan <shuah@kernel.org>
References: <20221017105502.307506-1-naveen.n.rao@linux.vnet.ibm.com>
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        <20221019001949.950fb044677f96c6cdd00fdf@kernel.org>
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        <1666172148.1jppmgndx2.naveen@linux.ibm.com>
        <20221020004607.a78c771e12ad0f65c018220b@kernel.org>
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Masami Hiramatsu wrote:
> On Wed, 19 Oct 2022 15:15:09 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
>=20
>> Steven Rostedt wrote:
>> > On Wed, 19 Oct 2022 00:19:49 +0900
>> > Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
>> >=20
>> >> > You need to make sure that the "pause-on-trace" option is set or tr=
acing_on
>> >> > is set to 0 (disabled). Otherwise, if the tracing is still active, =
then the
>> >> > reading of the trace file could potentially never end. =20
>> >>=20
>> >> initialize_ftrace() does this setting. So it must be set.
>> >> If you run the ftracetest on old kernel, this feature is not there an=
d
>> >> it may cause a trouble. Naveen, can you clarify it?
>>=20
>> Yes, the change to not pause on opening the trace file looks to be the=20
>> problem.
>>=20
>> >=20
>> > But for old kernels that do not have "pause-on-trace" it should be the
>> > default. The "pause-on-trace" was added when the default was changed t=
o not
>> > pause the trace while reading it.
>>=20
>> It looks like the kernel patch was picked up, but Masami's patch for the=
=20
>> selftest wasn't backported. I have requested a test with that applied.
>=20
> Good! That should be backported too.
> BTW, which kernel version do you test?

This was reported in internal tests with RHEL kernel.

>=20
>>=20
>> Separately, before I saw your response, I came up with the below patch=20
>> to update the selftests to disable tracing before reading the trace=20
>> file. I have also requested this to be tested.
>=20
> Yeah, OK. This also looks OK to me.

This patch doesn't seem to be enough - event/subsystem-enable.tc also=20
needs updates. In light of that, I'm not sure if the large number of=20
disable_tracing statements required makes sense. So, I'm inclined to=20
drop this patch in favour of the existing pause-on-trace option.


Thanks,
Naveen