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 3.16-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-3.16 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-3.16/powerpc-add-smp_mb-s-to-arch_spin_unlock_wait.patch
queue-3.16/powerpc-add-smp_mb-to-arch_spin_is_locked.patch
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