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powerpc: Add smp_mb()s to arch_spin_unlock_wait()

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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>
This commit is contained in:
Michael Ellerman 2014-08-07 15:36:18 +10:00 committed by Benjamin Herrenschmidt
parent 51d7d5205d
commit 78e05b1421
1 changed files with 4 additions and 0 deletions
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4
arch/powerpc/lib/locks.c
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@ -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);