linux-kernel - Re: [PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

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Date:	Thu, 18 Jun 2015 22:09:31 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
cc:	Kanaka Juvva <kanaka.d.juvva@...ux.intel.com>,
	glenn.p.williamson@...el.com, matt.fleming@...el.com,
	will.auld@...el.com, Andi Kleen <andi@...stfloor.org>,
	ananth.s.narayan@...el.com, LKML <linux-kernel@...r.kernel.org>,
	andrew.j.herdrich@...el.com, Tony Luck <tony.luck@...el.com>,
	Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
	mingo@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
	luto@...capital.net, dvlasenk@...hat.com, bp@...en8.de,
	peter.p.waskiewicz.jr@...el.com, imammedo@...hat.com, bp@...e.de,
	ross.zwisler@...ux.intel.com, jacob.w.shin@...il.com,
	dirk.j.brandewie@...el.com, vikas.shivappa@...el.com,
	edwin.verplanke@...el.com, tomasz.kantecki@...el.com
Subject: Re: [PATCH v1 2/2] x86, perf,cqm: handle CPU hotplug

On Thu, 18 Jun 2015, Dave Hansen wrote:
> On 06/18/2015 12:47 PM, Thomas Gleixner wrote:
> >> > @@ -1239,12 +1239,15 @@ static inline void cqm_pick_event_reader(int cpu)
> >> >  	int phys_id = topology_physical_package_id(cpu);
> >> >  	int i;
> >> >  
> >> > +	mutex_lock(&cache_mutex);
> > I already explained it to Vikas. You CANNOT take a mutex in that code
> > path as it runs with interrupts disabled on a CPU which cannot
> > schedule.
> 
> How did lockdep not blow up and scream about this?

Dunno. I did not test that stuff.

The might_sleep() in mutex_lock() should catch it as well, IF that
code was ever executed AFTER boot on a running system.

Thanks,

	tglx
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