Commit 78e05b14 authored Aug 07, 2014 by Michael Ellerman Committed by Benjamin Herrenschmidt Aug 13, 2014

powerpc: Add smp_mb()s to arch_spin_unlock_wait()



Similar to the previous commit which described why we need to add a
barrier to arch_spin_is_locked(), we have a similar problem with
spin_unlock_wait().

We need a barrier on entry to ensure any spinlock we have previously
taken is visibly locked prior to the load of lock->slock.

It's also not clear if spin_unlock_wait() is intended to have ACQUIRE
semantics. For now be conservative and add a barrier on exit to give it
ACQUIRE semantics.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

parent 51d7d520

arch/powerpc/lib/locks.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -70,12 +70,16 @@ void __rw_yield(arch_rwlock_t *rw)

		void arch_spin_unlock_wait(arch_spinlock_t *lock)
		{
		smp_mb();

		while (lock->slock) {
		HMT_low();
		if (SHARED_PROCESSOR)
		__spin_yield(lock);
		}
		HMT_medium();

		smp_mb();
		}

		EXPORT_SYMBOL(arch_spin_unlock_wait);

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