Backported from 78e05b1421fa upstream, for stable 3.14 and 3.16.
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@xxxxxxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/lib/locks.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
index 0c9c8d7d0734..170a0346f756 100644
--- a/arch/powerpc/lib/locks.c
+++ b/arch/powerpc/lib/locks.c
@@ -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);
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html