linux-kernel - Re: Spinlock query

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Date:	Wed, 30 Aug 2006 11:01:43 +0530
From:	"Rajat Jain" <rajat.noida.india@...il.com>
To:	"Rik van Riel" <riel@...riel.com>
Cc:	"Rick Brown" <rick.brown.3@...il.com>, kernelnewbies@...linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: Spinlock query

On 8/30/06, Rik van Riel <riel@...riel.com> wrote:
> Rick Brown wrote:
> > Hi,
> >
> > In my driver (Process context), I have written the following code:
> >
> > --------------------------------------------
> > spin_lock(lock)
> > ...
> > //Critical section to manipulate driver data
>
> ... interrupt hits here
>     interrupt handler tries to grab the spinlock, which is already taken
>     *BOOM*
>
> > spin_u lock(lock)
> > ---------------------------------------------
> >

The interrupt handler TRIES to grab the spinlock, which is already
taken. Why will it "BOOM"? Wouldn't the interrupt handler busy wait,
waiting for the lock?

Am I missing something here?

Rajat

> > I have written similar code in my interrupt handler (Interrupt
> > context). The driver data is not accessed from anywhere else. Is my
> > code safe from any potential concurrency issues? Is there a need to
> > use spin_lock_irqsave()? In both the places?
>
> You need to use spin_lock_irqsave() from process context.
>  From the interrupt handler itself it doesn't hurt, but it
> shouldn't matter much since interrupt handlers should not
> get preempted.
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