So we will hit NMI watchdog even if spinlock is acquired.
On Fri, Jan 7, 2011 at 11:57 AM, Tayade, Nilesh <Nilesh.Tayade@xxxxxxxxxxxx> wrote:
Hi,
> -----Original Message-----
> From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [mailto:kernelnewbies-
> bounces@xxxxxxxxxxxxxxxxx] On Behalf Of Dave Hylands
> Sent: Friday, January 07, 2011 10:59 AM
> To: Viral Mehta
> Cc: kernelnewbies@xxxxxxxxxxxxxxxxx
> Subject: Re: spin_lock and scheduler confusion
>
> Hi Viral,
>
> On Wed, Jan 5, 2011 at 2:23 PM, Viral Mehta
> <Viral.Mehta@xxxxxxxxxxxxxxx> wrote:
> >
> > Hi ,
> >
> > I need your help to solve below confusion.
> >
[...]
>
> Note that you can't sleep while you hold a spinlock. You're not
> allowed to perform any type of blocking operations. If you're holding
> the spinlock for any significant length of time, then you're using the
> wrong design.
>
> > spin_lock_irqrestore();
> > 3. One of the CPU core tries to execute this code and so acquires the
> lock.
> > 4. Now, second core is also goes to execute same piece of code and so
> will
[...]
>
> Not while it's holding the spinlock or waiting for the spinlock.
>
> > Ever if timeslice is over for the current task ?
>
> The time tick interrupt is what determines when the timeslice is over.
> Since you have interrupts disabled, the timer interrupt can't happen.
>
> > What if scheduler code is running on CPU core-3 and sees that
> > timeslice for task running on CPU core-2 has expired ?
>
> Each core only considers the timeslices for its own core.
>
> > I guess timeslice expire case is not as same as preemption. Or may be
> I am
> > terribly wrong.
>
> You shouldn't be holding a spinlock for periods of time approaching
> the length of a timeslice. The timer interrupt is what determines the
> end of a timeslice. No timer interrupt, no end of a timeslice.
> Preemption is also triggered by the timer interrupt, or by releasing a
> resource that a higher priority task is waiting for.
May be my understanding is incorrect, but wouldn't we hit the NMI watchdog here(assuming we are running on x86/x86_64)?
We have a system lockup for long time.
http://lxr.linux.no/#linux+v2.6.37/Documentation/nmi_watchdog.txt
Could someone please clarify?
>
> Dave Hylands
--
Thanks,
Nilesh
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