From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Murray <andrew.murray@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Rik van Riel <riel@surriel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] smp,cpumask: Don't call functions on offline CPUs
Date: Wed, 22 May 2019 16:49:18 +0200 [thread overview]
Message-ID: <20190522144918.GH16275@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20190522143711.GC8268@e119886-lin.cambridge.arm.com>
On Wed, May 22, 2019 at 03:37:11PM +0100, Andrew Murray wrote:
> > Is perhaps the problem that on_each_cpu_cond() uses cpu_onlne_mask
> > without protection?
>
> Does this prevent racing with a CPU going offline? I guess this prevents
> the warning at the expense of a lock - but is only beneficial in the
> unlikely path. (In the likely path this prevents new CPUs going offline
> but we don't care because we don't WARN if they aren't they when we
> attempt to call functions).
>
> At least this is my limited understanding.
Hmm.. I don't think it could matter, we only use the mask when
preempt_disable(), which would already block offline, due to it using
stop_machine().
So the patch is a no-op.
What's the WARN you see? TLB invalidation should pass mm_cpumask(),
which similarly should not contain offline CPUs I'm thinking.
next prev parent reply other threads:[~2019-05-22 14:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 11:15 [PATCH] smp,cpumask: Don't call functions on offline CPUs Andrew Murray
2019-05-22 14:09 ` Peter Zijlstra
2019-05-22 14:37 ` Andrew Murray
2019-05-22 14:49 ` Peter Zijlstra [this message]
2019-05-22 15:14 ` Andrew Murray
2019-05-27 10:52 ` Peter Zijlstra
2019-05-22 18:23 ` Rik van Riel
2019-05-27 10:53 ` Peter Zijlstra
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