Patch "powerpc: Add smp_mb()s to arch_spin_unlock_wait()" has been added to the 3.14-stable tree

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This is a note to let you know that I've just added the patch titled

    powerpc: Add smp_mb()s to arch_spin_unlock_wait()

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-add-smp_mb-s-to-arch_spin_unlock_wait.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 78e05b1421fa41ae8457701140933baa5e7d9479 Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Date: Thu, 7 Aug 2014 15:36:18 +1000
Subject: powerpc: Add smp_mb()s to arch_spin_unlock_wait()

From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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);


Patches currently in stable-queue which might be from mpe@xxxxxxxxxxxxxx are

queue-3.14/powerpc-add-smp_mb-s-to-arch_spin_unlock_wait.patch
queue-3.14/powerpc-add-smp_mb-to-arch_spin_is_locked.patch
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