linux-kernel - Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock + local_irq_save, especially when CONFIG

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Message-ID: <51C2E083.7080302@asianux.com>
Date:	Thu, 20 Jun 2013 18:59:15 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock
 + local_irq_save, especially when CONFIG_LOCKDEP not defined

On 06/20/2013 06:42 PM, Thomas Gleixner wrote:
> Chen,
> 
> On Thu, 20 Jun 2013, Chen Gang wrote:
>> > On 06/20/2013 05:07 PM, Thomas Gleixner wrote:
>>> > > If A is semantically the same as B, then B is semantically the same as
>>> > > A. At least that's the common understanding.
>>> > > 
>> > 
>> >   From A to B is OK.
>> > 
>> > Not means:
>> > 
>> >   From B to A is also OK.
> Either you're questioning logic, math and fundamental basics of
> computer science or you simply fail to grok the difference between
> semantics and implementation details. See below.
> 
>>> > > Yes, it depends on the implementation, but all implementations do:
>>> > > 
>>> > >      local_irq_save(flags);
>>> > >      arch_spin_lock_flags(l, flags);
>>> > > 
>> > 
>> > Yes this is spin_lock_irqsave().
>> > 
>> > At least, this implemenation is not equal to.
>> > 
>> > 	local_irq_save(flags);
>> > 	spin_lock(l);
> Again. It is semantically the same, because the semantics are:
> 
>    spin_lock_irqsave() returns with interrupts disabled, preemption
>    disabled and the lock acquired.
> 
> This construct exactly follows these semantics:
> 
>  	local_irq_save(flags);
>  	spin_lock(l);
> 
> After spin_lock(l) interrupts are disabled, preemption is disabled and
> the lock is acquired. End of discussion.
> 

OK, end of discussion. It is a polite.


> I wasted enough time explaining you the difference between semantics
> and implementation, but you seem to be simply advisory restistant.
> 

Yes, time resources are really very expensive for every members.


> And I already told you very impolite in the other thread, that I'm not
> going to cope with such nonsense anymore. And yes, I'm tired of it.
> 

OK, I don't care about it.

We just stop now.

:-)

> Provide factual prove, that there is a bug in the code. And to prove
> that, you actually need to understand the code and the basic concepts
> behind it. 
> 
> If you keep up pursuing your contributions plan at the expense of my
> and other peoples valuable time, I consider this as extremly impolite
> from your side. The form of collaboration you are going to achieve
> this way is an entry in my /dev/null mail filter.


Don't worry about it, and why worry about it ?


Thanks.
-- 
Chen Gang

Asianux Corporation
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