linux-kernel - Re: Spinlocks waiting with interrupts disabled / preempt disabled.

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Message-ID: <Pine.LNX.4.64.0805071002330.3110@schroedinger.engr.sgi.com>
Date:	Wed, 7 May 2008 10:04:39 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Spinlocks waiting with interrupts disabled / preempt disabled.

On Wed, 7 May 2008, Ingo Molnar wrote:

> > +		return flags;
> > +	local_irq_restore(flags);
> > +	while (!write_can_lock(lock))
> > +		cpu_relax();
> > +	goto retry;
> >  }
> >  EXPORT_SYMBOL(_write_lock_irqsave);
> 
> hm, this is done on a too high level and will turn off some debugging 
> code. I.e. if we dont just loop long but truly deadlock here we wont 
> call lib/spinlock_debug.c's _raw_write_lock() code that does some sanity 
> checks in the debug case.

Right. I guessed that given the gazillion helper functions and wanted to 
know how to address this in the right way.

> so how about doing this on a deeper level and adding a new 
> __raw_write_lock_flags() primitive that would look at the flags value 
> and could enable interrupts in the lowlevel code?

Ok will look at that. Note that this is not unique to _write_lock_irqsave 
but all other locks that disable interrupts seem to have the same issue. 

We are likely going to duplicate a lot of functions.


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