Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Valentin Schneider <vschneid@redhat.com>
To:     Vincent Donnefort <vdonnefort@google.com>
Cc:     peterz@infradead.org, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, regressions@leemhuis.info,
        kernel-team@android.com, Derek Dolney <z23@posteo.net>
Subject: Re: [PATCH v4] cpu/hotplug: Do not bail-out in DYING/STARTING sections
In-Reply-To: <YtbSP21k1hTKGlqv@google.com>
References: <20220704131346.2650163-1-vdonnefort@google.com>
 <xhsmhfsix6ssc.mognet@vschneid.remote.csb> <YtbSP21k1hTKGlqv@google.com>
Date:   Fri, 22 Jul 2022 19:35:34 +0100
Message-ID: <xhsmhilnpf11l.mognet@vschneid.remote.csb>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On 19/07/22 16:48, Vincent Donnefort wrote:
> On Tue, Jul 19, 2022 at 04:12:03PM +0100, Valentin Schneider wrote:
>> On 04/07/22 14:13, Vincent Donnefort wrote:
>> > +static int _cpuhp_invoke_callback_range(bool bringup,
>> > +					unsigned int cpu,
>> > +					struct cpuhp_cpu_state *st,
>> > +					enum cpuhp_state target,
>> > +					bool nofail)
>> [...]
>> > +		if (nofail) {
>> > +			pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
>> > +				cpu, bringup ? "UP" : "DOWN",
>> > +				cpuhp_get_step(st->state)->name,
>> > +				st->state, err);
>> > +			ret = -1;
>>
>> On a single failure we'll get two warns (WARN_ON_ONCE() + pr_warn(), and
>> then subsequently just the pr_warn()), is that intended?
>
> It does, this is to keep the backtrace that used to be here... but now, giving
> a second thought, we can probably get rid of it and just keep the pr_warn()?
>
>>
>> Also, why not have ret = err here?
>
> If two states fail, the ret wouldn't mean much, hence a default "-1" just for
> the WARN_ONCE.

Right

> But if we drop the latter, that would simplify the problem of
> knowing which error code to return.
>

We need to drop one of the two, the pr_warn() will probably be more useful
if/when we need to debug this, so go for it.