linux-kernel - Re: [patch 1/6] x86, ftrace, hw-branch-tracer: support hotplug cpus

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Message-ID: <20090224193622.GA26734@elte.hu>
Date:	Tue, 24 Feb 2009 20:36:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Markus Metzger <markus.t.metzger@...el.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, hpa@...or.com,
	markus.t.metzger@...il.com, srostedt@...hat.com
Subject: Re: [patch 1/6] x86, ftrace, hw-branch-tracer: support hotplug cpus


* Markus Metzger <markus.t.metzger@...el.com> wrote:

> Support hotplug cpus.

> +static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
> +				     unsigned long action, void *hcpu)
> +{
> +	unsigned int cpu = (unsigned long)hcpu;
> +
> +	mutex_lock(&bts_tracer_mutex);

This is buggy: CPU hotplug handlers must not sleep (they are 
called with irqs disabled), while this code does a mutex_lock() 
which can sleep.

	Ingo
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