Re: [PATCH] improve spinlock debugging

[Manfred Spraul]

george anzinger wrote:
> 
> Manfred Spraul wrote:
> >
> > CONFIG_DEBUG_SPINLOCK only adds spinlock tests for SMP builds. The
> > attached patch adds runtime checks for uniprocessor builds.
> >
> > Tested on i386/UP, but it should work on all platforms. It contains
> > runtime checks for:
> >
> > - missing initialization
> > - recursive lock
> > - double unlock
> > - incorrect use of spin_is_locked() or spin_trylock() [both function
> > do not work as expected on uniprocessor builds]
> > The next step are checks for spinlock ordering mismatches.
> 
> What do you consider an order mismatch?  I would like to see this:
>
	spin_lock(a);
	spin_lock(b);

and somewhere else
	spin_lock(b);
	spin_lock(a);

> 
> Run time checks for xxx_irq when irq is already off seem reasonable.
> The implication is that the xxx_unlockirq will then turn it on, which
> most likely is an error.  Also, see above about rolling assumptions in
> to the macro name.
>
Unfortuantely there are still a few special cases where spin_lock_irq()
with already disabled interrupts is both intentional and correct^wnot
buggy (search for sleep_on and cli() through the lkml archives).

And there are optimizations such as
	spin_lock_bh(a);
	spin_unlock(b);
	spin_lock(b);
	spin_unlock_bh(b);

--
	Manfred