Re: [PATCH] Prevent spinlock debug from timing out too early

[Ingo Molnar <mingo@elte.hu>]

* Andi Kleen <ak@suse.de> wrote:

> > a better solution would be to call __delay(1) after the first failed 
> > attempt, that would make the delay at least 1 second long. It seems 
> > __delay() is de-facto exported by every architecture, so we can rely on 
> > it in the global spinlock code.
> > 
> > So how about the patch below instead?
> 
> Are you sure loops_per_jiffie is always in delay(1) units?

there are a few explicit calls to __delay() in drivers/*, so i'd assume 
so. A grep also seems to suggest so:

 ./ppc/xmon/xmon.c:extern inline void __delay(unsigned int loops)
 ./x86_64/lib/delay.c:void __delay(unsigned long loops)
 ./sparc64/lib/delay.c:void __delay(unsigned long loops)
 ./sh64/lib/udelay.c:void __delay(int loops)
 ./m32r/lib/delay.c:void __delay(unsigned long loops)
 ./i386/lib/delay.c:void __delay(unsigned long loops)
 ./s390/lib/delay.c:void __delay(unsigned long loops)
 ./sh/lib/delay.c:void __delay(unsigned long loops)
 ./powerpc/kernel/time.c:void __delay(unsigned long loops)

but yes, this is a non-specified thing so far, so there could be 
problems on some platforms. Worst-case we never time out - which could 
be detected via the NMI watchdog or the soft-lockup watchdog - so it's 
not like they would go unnoticed.

	Ingo