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SubjectRe: *_trylock return on success?
On Saturday 25 November 2000 18:49, Rik van Riel wrote:
> On Sat, 25 Nov 2000, Roger Larsson wrote:
> > Questions:
> > What are _trylocks supposed to return?
>
> It depends on the type of _trylock ;(
>
> > Does spin_trylock and down_trylock behave differently?
> > Why isn't the expected return value documented?
>
> The whole trylock stuff is, IMHO, a big mess. When you
> change from one type of trylock to another, you may be
> forced to invert the logic of your code since the return
> code from the different locks is different.
>
> For bitflags, for example, the trylock returns the state
> the bit had before the lock (ie. 1 if the thing was already
> locked).
>

This holds for down_trylocks too.
It looks like it is the spinlocks that are wrong... :-(

As most return values tend to be error returns that also
matches other code in functionallity.

>
> For spinlocks, it'll probably return something else ;/
It does...

I guess fixing this is too much too late?


It looks like ppc mixes the ways... from arch/ppc/lib/locks.c:46

int spin_trylock(spinlock_t *lock)
{
if (__spin_trylock(&lock->lock)) /* one on failure */
return 0; /* zero on failure */
lock->owner_cpu = smp_processor_id();
lock->owner_pc = (unsigned long)__builtin_return_address(0);
return 1;
}


BUT anyway...
The thing I hit is not a bug in the kernel proper - it is in the preemptive
stuff.

/RogerL

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