linux-kernel - Re: [PATCH 3/3] smp/ipi:Remove check around csd lock in handler for smp_call

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Date:	Sun, 07 Jul 2013 21:53:48 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Wang YanQing <udknight@...il.com>, mingo@...e.hu,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, deepthi@...ux.vnet.ibm.com,
	peterz@...radead.org, rusty@...tcorp.com.au,
	heiko.carstens@...ibm.com, rostedt@...dmis.org, miltonm@....com,
	srivatsa.bhat@...ux.vnet.ibm.com, tj@...nel.org,
	akpm@...ux-foundation.org, svaidy@...ux.vnet.ibm.com,
	shli@...nel.org, tglx@...utronix.de, lig.fnst@...fujitsu.com,
	anton@...ba.org
Subject: Re: [PATCH 3/3] smp/ipi:Remove check around csd lock in handler for
 smp_call_function variants

Hi Wang,

On 07/06/2013 07:51 PM, Wang YanQing wrote:
> On Sat, Jul 06, 2013 at 01:36:27PM +0530, Preeti U Murthy wrote:
>> Ideally it should be under a WARN_ON(). csd_unlock() has that WARN_ON().
>> Unlocking a parameter which is not locked should be seen as a bug, which
>> the above code is not doing. In fact it avoids it being reported as a bug.
> 
> Although I know what's your meaning, but just like the comment in code:
> 
> "
>  /*                                                                                               
>   * Unlocked CSDs are valid through generic_exec_single():                                        
>   */

I don't understand this comment. All callers of generic_exec_single()
take the csd lock. So where is the scenario of csds being unlocked in
generic_exec_single() before the call to
arch_send_call_function_single_ipi() is made?
  Rather what is the above comment trying to say?

> "
> 
> If the csd don't come from generic_exec_single, then
> Unlocked CSDs maybe are not valid. So we check CSD_FLAG_LOCK
> to avoid trigger the WARN_ON in csd_unlock.
> 
> Genric_exec_single's name imply it is a generic version,
> you know, maybe we will have "special" version.
> 
> Thanks.
> 

Regards
Preeti U Murthy

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