[PATCH 1/3] arm/arm64: spinlocks: fix memory barriers

[Andrew Jones <drjones@xxxxxxxxxx>]

It shouldn't be necessary to use a barrier on the way into
spin_lock. We'll be focused on a single address until we get
it (exclusively) set, and then we'll do a barrier on the way
out. Also, it does make sense to do a barrier on the way in
to spin_unlock, i.e. ensure what we did in the critical section
is ordered wrt to what we do outside it, before we announce that
we're outside.

Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
---
 lib/arm/spinlock.c   | 8 ++++----
 lib/arm64/spinlock.c | 5 ++---
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/arm/spinlock.c b/lib/arm/spinlock.c
index 3b023ceaebf71..116ea5d7db930 100644
--- a/lib/arm/spinlock.c
+++ b/lib/arm/spinlock.c
@@ -7,10 +7,9 @@ void spin_lock(struct spinlock *lock)
 {
 	u32 val, fail;
 
-	dmb();
-
 	if (!mmu_enabled()) {
 		lock->v = 1;
+		smp_mb();
 		return;
 	}
 
@@ -25,11 +24,12 @@ void spin_lock(struct spinlock *lock)
 		: "r" (&lock->v)
 		: "cc" );
 	} while (fail);
-	dmb();
+
+	smp_mb();
 }
 
 void spin_unlock(struct spinlock *lock)
 {
+	smp_mb();
 	lock->v = 0;
-	dmb();
 }
diff --git a/lib/arm64/spinlock.c b/lib/arm64/spinlock.c
index 68b68b75ba60d..a3907f03cacda 100644
--- a/lib/arm64/spinlock.c
+++ b/lib/arm64/spinlock.c
@@ -13,10 +13,9 @@ void spin_lock(struct spinlock *lock)
 {
 	u32 val, fail;
 
-	smp_mb();
-
 	if (!mmu_enabled()) {
 		lock->v = 1;
+		smp_mb();
 		return;
 	}
 
@@ -35,9 +34,9 @@ void spin_lock(struct spinlock *lock)
 
 void spin_unlock(struct spinlock *lock)
 {
+	smp_mb();
 	if (mmu_enabled())
 		asm volatile("stlrh wzr, [%0]" :: "r" (&lock->v));
 	else
 		lock->v = 0;
-	smp_mb();
 }
-- 
2.4.3

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