On Wed, Aug 24, 2016 at 05:34:12PM +0200, Peter Zijlstra wrote: > On Wed, Aug 24, 2016 at 10:56:59AM +0100, Will Deacon wrote: > > > + owner = atomic_long_read(&lock->owner); > > > + for (;;) { > > > + unsigned long old; > > > + > > > + old = atomic_long_cmpxchg_release(&lock->owner, owner, owner & > > > 0x03); > > > + if (old == owner) > > > + break; > > > + > > > + owner = old; > > > + } > > > > Can you rewrite this using atomic_long_fetch_and_release? > > Yes, until patch 3/3.. but now that you mention it I think we can do: > > owner = atomic_long_read(&lock->owner); > if (!(owner & MUTEX_FLAG_HANDOFF)) > (void)atomic_long_fetch_and_release(MUTEX_FLAGS, &lock->owner); >
And of course, x86 would very much like atomic_long_and_release() here, such that it can do LOCK ADD instead of a LOCK CMPXCHG loop. But of course, we don't have that ...