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

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Date:	Mon, 8 Jul 2013 01:25:41 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc:	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

On Sun, Jul 07, 2013 at 09:53:48PM +0530, Preeti U Murthy wrote:
> > "
> >  /*                                                                                               
> >   * 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?

I have given the answer to this question in last reply.

I don't know whether it is right to make a assumption through
this way that what you do currently:

Find all the current api users, and drop all the robust codes,
despite the unpredictable future users.

Ok, I know the balance between "robust" vs "performance",
robust check codes will bring performance penalty in fastest
code path, but the "penalty" is neglectable sometimes for
modern CPU.

I decide to respect the MAINTAINER's decision to accept this 
change or not.

Thanks.



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