| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.16 286/357] powerpc: Add smp_mb()s to arch_spin_unlock_wait() | Date | Fri, 3 Oct 2014 14:31:12 -0700 |
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3.16-stable review patch. If anyone has any objections, please let me know.
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From: Michael Ellerman <mpe@ellerman.id.au>
commit 78e05b1421fa41ae8457701140933baa5e7d9479 upstream.
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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/powerpc/lib/locks.c | 4 ++++ 1 file changed, 4 insertions(+)
--- 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);
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