spin_lock and scheduler confusion

[anish singh]

On Fri, Jan 7, 2011 at 1:19 PM, nilesh <nilesh.tayade at netscout.com> wrote:

> On Fri, 2011-01-07 at 13:05 +0530, Rajat Sharma wrote:
> > As I remember timer interrupt as well is an NMI so, it is possible
> > (although not advised) to call schedule function while holding
> > spinlock on same core.
> >
> > spin_lock_irqsave();
> > schedule();
> > spin_lock_irqrestore();
> >
> > however if you have debugging options turned on like
> > CONFIG_DEBUG_SPINLOCK, you may likely get kernel warning for
> > 'scheduling in atomic context'.
> >
> > Then what can happen if this core is allowed to switched to new
> > process? Consider the case where new process as well tries to aquire
> > same spin_lock() which new process can not aquire and start spinning
> > for the lock for ever :). Likewise, other cores will also get locked
> > down.
> >
> > However stil you can detect softlockup through NMI watchdog.
>
> >>Sorry if I am building up the confusion here. But as Dave Hylands
> >>initially mentioned, there will be no timer interrupt. So shouldn't the
> >>NMI watchdog get triggered then? No interrupts -> system freeze -> NMI
> >>Wdt reboot.
>

In my opinion(uninformed ) NMI watchdog will be triggered only in case where
you are holding a spinlock.It will not be triggered just because timer
interrupts are disabled due to holding a spinlock.
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