linux-kernel - Re: [PATCH v2] oprofile: add SMP barriers for hrtimer hotplug code

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Message-ID: <AANLkTimBTrqOk_ctBKmT0c=teZ8oG3c7Ai6-BmZwOj+g@mail.gmail.com>
Date:	Tue, 1 Feb 2011 16:03:54 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org,
	oprofile-list@...ts.sf.net, Robert Richter <robert.richter@....com>
Subject: Re: [PATCH v2] oprofile: add SMP barriers for hrtimer hotplug code

Hi,

2011/2/1 Santosh Shilimkar <santosh.shilimkar@...com>:
>> -----Original Message-----
>> From: Will Deacon [mailto:will.deacon@....com]
>> diff --git a/drivers/oprofile/timer_int.c
>> b/drivers/oprofile/timer_int.c
>> index 0107251..a3a94ea 100644
>> --- a/drivers/oprofile/timer_int.c
>> +++ b/drivers/oprofile/timer_int.c
>> @@ -48,6 +48,7 @@ static int oprofile_hrtimer_start(void)
>>  {
>>       get_online_cpus();
>>       ctr_running = 1;
>> +     smp_mb();
>>       on_each_cpu(__oprofile_hrtimer_start, NULL, 1);

Just a little question:

Before calling __oprofile_hrtimer_start in other CPUs,
there have been some smp_mb executed already, such as called by
smp_call_function_many in current CPU, and called by
generic_smp_call_function_interrupt in the func-calling CPU,
so are these smp_mb enough for correct order of access
for 'ctr_running' ?

>>       put_online_cpus();
>>       return 0;

thanks,
-- 
Lei Ming
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