linux-kernel - Re: raw_spinlock

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Message-ID: <4C963DAC.4040604@redhat.com>
Date:	Sun, 19 Sep 2010 18:43:24 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: raw_spinlock_t rules

  On 09/19/2010 06:38 PM, Steven Rostedt wrote:
> On Sun, 2010-09-19 at 15:09 +0200, Avi Kivity wrote:
> >  Some time ago, the i8259 emulation code in kvm was changed to use
> >  raw_spinlock_t, as it was called in a preempt_disable() and
> >  local_irq_disable() context, which doesn't work with preemptible
> >  spinlocks used with CONFIG_PREEMPT_RT.
> >
> >  In Linux 2.6.37, the spinlock will no longer be taken in these contexts,
> >  so I'd like to change it to a normal spinlock_t.  However, it is still
> >  taken in a spin_lock_irq() context.
> >
> >  Is it okay to do this change?  I figured since spin_lock_irq() is part
> >  of the spinlock infrastructure it might to the right thing.
> >
>
> In PREEMPT_RT all interrupts (besides the timer) is converted to a
> thread. The spin_lock_irq() will not disable interrupts in PREEMPT_RT,
> because it is not needed (irqs are threaded and wont cause a deadlock if
> they share the same spin_locks).
>
> Note, spin_locks used by the timer will must be raw_spin_lock(), and
> threaded context must disable interrupts for real before using it.
>

Thanks.  So it looks like we can convert that spinlock.

-- 
error compiling committee.c: too many arguments to function

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