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Message-ID: <51C2D10B.5030408@asianux.com>
Date: Thu, 20 Jun 2013 17:53:15 +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 05:07 PM, Thomas Gleixner wrote:
> On Thu, 20 Jun 2013, Chen Gang wrote:
>> > On 06/19/2013 06:53 PM, Thomas Gleixner wrote:
>>> > > So
>>> > > local_irq_save(flags);
>>> > > spin_lock(&lock);
>>> > >
>>> > > is semantically the same as
>>> > >
>>> > > spin_lock_irqsave(&lock, flags);
>>> > >
>> >
>> > Yes (but reverse is NO).
>> >
>>> > > And this is completely independent of LOCKDEP.
>> >
>> > NO.
>> >
>> > spin_lock_irqsave(&lock, flags);
>> >
>> > is not semantically the same as
>> >
>> > local_irq_save(flags);
>> > spin_lock(&lock);
> 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.
> You seem to have a different definition of semantics, but I prefer the
> common one.
>
>> > It depend on the spin_lock_irqsave() implementation, if the parameters
>> > has no relation ship with each other, semantically the same.
> 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);
So if for arch_spin_lock_flags(), 'flags' is no relation ship with 'l',
we can say semantically the same.
Thanks.
--
Chen Gang
Asianux Corporation
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