Re: [uml-devel] Re: TLS support - status - need for re-testing

[Blaisorblade <blaisorblade@yahoo.it>]

On Friday 24 March 2006 18:32, Jeff Dike wrote:
> On Fri, Mar 24, 2006 at 12:43:33PM +0100, Blaisorblade wrote:
> > We discussed this time ago, and read the description of the patch:

> > > global-ldt-sem - We should be using mutexes now, not semaphores
> >
> > That's your patch, but below I drop this.
>
> My patch predates mutexes.
>
> But you still use semaphores, and that should be updated.

We'll do it at some time, there's no hurry for that; or they'll do it anyway 
before ripping out semaphores.

> It's simpler.  A single global lock is simpler than a lock in every
> datastructure.

My only doubt (I'd almost swear it doesn't happen) is if two locks of two 
different structures are ever taken. That would fail.

About locking, I've discovered that sigio_lock must use spin_lock_irqsave() 
instead of spin_lock; currently with Mutex debugging I get hangs on that 
spinlock, but on UP currently you get a race between process context and 
interrupt context.

The failing case is when that lock is taken in process context, then an 
interrupt is triggered whose handler takes again that. In fact, for mutual 
exclusion between process context and irq context an spin_lock_irq{,save} is 
_always_ recommended.

Only problem will be to check for sleepers in process context - there could be 
many ones.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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