RE: [PATCH] Fix data race in mark_rt_mutex_waiters

[David Laight]

From: Peter Zijlstra
> Sent: 20 January 2023 16:23
...
> >  	do {
> > -		owner = *p;
> > +		owner = READ_ONCE(*p);
> >  	} while (cmpxchg_relaxed(p, owner,
> >  				 owner | RT_MUTEX_HAS_WAITERS) != owner);
> >
> 
> Can't we replace the whole of that function with:
> 
> 	set_bit(0, (unsigned long *)&lock->owner);
> 
> ?

If you need the cast then probably not...

There really ought to be a compile-time test (somehow)
that set_bit() is only used on large bit arrays.

OTOH atomic_or32/64() and atomic_and32/64() might use
usable in many places.

On x86 I doubt it makes much difference whether you use
'bis' or 'lock or'.

	David

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