RE: [PATCH] Fix data race in mark_rt_mutex_waiters

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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