Re: [PATCH] kernel/timer.c: using spin_lock_irqsave instead of spin_lock+ local_irq_save, especially when CONFIG_LOCKDEP not defined
From: Chen Gang
Date: Thu Jun 20 2013 - 04:38:16 EST
On 06/19/2013 06:53 PM, Thomas Gleixner wrote:
> On Wed, 19 Jun 2013, Chen Gang wrote:
>> > On 06/19/2013 05:59 PM, Thomas Gleixner wrote:
>>> > > I'm well aware how that works. And there is no difference whether you
>>> > > do:
>>> > >
>>> > > local_irq_save(flags);
>>> > > spin_lock(&lock);
>>> > > or
>>> > > spin_lock_irqsave(&lock, flags);
>> > if CONFIG_LOCKDEP is not defined, they are not semantically the same.
> Care to explain _your_ spinlock semantics to me?
> The factual ones are:
> spin_lock_irqsave() returns with the lock held, interrupts and
> preemption disabled.
> spin_lock() returns with the lock held, preemption disabled. It
> does not affect interrupt disabled/enabled state
> is semantically the same as
> spin_lock_irqsave(&lock, flags);
Yes (but reverse is NO).
> And this is completely independent of LOCKDEP.
is not semantically the same as
It depend on the spin_lock_irqsave() implementation, if the parameters
has no relation ship with each other, semantically the same.
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