Re: [patch] scheduler fixes, 2.5.32-BK

[Ingo Molnar]

On Fri, 30 Aug 2002, Linus Torvalds wrote:

> So why couldn't this happen? This is what used to happen before, I don't
> see that consolidating the spinlock had any impact at all.
> 
> 	CPU #0						CPU #1
> 
> 	down()						up()
> 
> 		lock decl (negative)
> 		__down()				lock incl
> 			spinlock()			__up()
> 			atomic_add_negative()
> 				success - break
> 			spinunlock();
> 		}					wake_up()
> 	return - semaphore is now invalid		spin_lock()
> 
> 							BOOM!

hm, indeed, you are right - completions are the only safe method.

i'm starting to wonder whether it's possible at all (theoretically) to
have a mutex design which has the current semaphore implementation's good
fastpath properties, but could also be used on stack.

	Ingo