spin_lock and scheduler confusion

[nilesh]

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. 

http://slacksite.com/slackware/nmi.html

> 
> Rajat

-- 
Thanks,
Nilesh