linux-kernel - Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up at boot time

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Message-ID: <20190617190552.GA10264@lerouge>
Date:   Mon, 17 Jun 2019 21:05:53 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nicholas Piggin <npiggin@...il.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kernel/isolation: Asset that a housekeeping CPU comes up
 at boot time

On Mon, Jun 17, 2019 at 05:59:31PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 10, 2019 at 05:24:32PM +1000, Nicholas Piggin wrote:
> > Nicholas Piggin's on June 1, 2019 9:39 pm:
> > > With the change to allow the boot CPU0 to be isolated, it is possible
> > > to specify command line options that result in no housekeeping CPU
> > > online at boot.
> > > 
> > > An 8 CPU system booted with "nohz_full=0-6 maxcpus=4", for example.
> > > 
> > > It is not easily possible at housekeeping init time to know all the
> > > various SMP options that will result in an invalid configuration, so
> > > this patch adds a sanity check after SMP init, to ensure that a
> > > housekeeping CPU has been onlined.
> > > 
> > > The panic is undesirable, but it's better than the alternative of an
> > > obscure non deterministic failure. The panic will reliably happen
> > > when advanced parameters are used incorrectly.
> > 
> > Ping on this one? This should resolve Frederic's remaining objection
> > to the series (at least until he solves it more generally).
> > 
> > As the series has already been merged, should we get this upstream
> > before release?
> 
> I was hoping for feedback from Frederic, lacking that, I've queued it
> now.
> 

Sorry I just came back from vacation. Any chance we can use a WARN() instead?
I prefer to use panic() only when data is really threatened or such.

Thanks.