On Thu, Jun 25, 2015 at 06:12:17PM +0200, Andrew Jones wrote:
> 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
>
looks good to me
-Christoffer
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