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

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Message-ID: <alpine.DEB.2.10.1506191716300.32420@vshiva-Udesk>
Date:	Tue, 23 Jun 2015 13:32:42 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Kanaka Juvva <kanaka.d.juvva@...ux.intel.com>,
	"Juvva, Kanaka D" <kanaka.d.juvva@...el.com>,
	"Williamson, Glenn P" <glenn.p.williamson@...el.com>,
	Matt Fleming <matt.fleming@...el.com>,
	"Auld, Will" <will.auld@...el.com>, andi@...stfloor.org,
	ananth.s.narayan@...el.com, linux-kernel@...r.kernel.org,
	"Herdrich, Andrew J" <andrew.j.herdrich@...el.com>,
	tony.luck@...el.com, peterz@...radead.org, x86@...nel.org,
	mingo@...hat.com, hpa@...or.com, luto@...capital.net,
	dvlasenk@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	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,
	"Verplanke, Edwin" <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, Thomas Gleixner wrote:

> On Thu, 18 Jun 2015, Kanaka Juvva wrote:
>
>> Added lock in event reader function. The cqm_pick_event_reader() function
>> accesses cqm_cpumask and it is critical section between this and
>> cqm_stable().
>>
>> This situation is true when a CPU is hotplugged. Mutex is used to protect
>> the critical section.
>>
>> Signed-off-by: Kanaka Juvva <kanaka.d.juvva@...ux.intel.com>
>> ---
>>  arch/x86/kernel/cpu/perf_event_intel_cqm.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
>> index 1880761..e17e37f 100644
>> --- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
>> +++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
>> @@ -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.

This patch also needs to be merged with the new package mask changes that 
was added. 
Will merge and send the fix.

Thanks,
Vikas

>
> Sigh.
>
> 	tglx
>
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