From ea818ea8340c13742a4f41e6077f732291aea4bc Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 25 Aug 2014 15:43:40 -0400
Subject: [PATCH] add working a_spin() atomic for non-x86 targets

conceptually, a_spin needs to be at least a compiler barrier, so the
compiler will not optimize out loops (and the load on each iteration)
while spinning. it should also be a memory barrier, or the spinning
thread might keep spinning without noticing stores from other threads,
thus delaying for longer than it should.

ideally, an optimal a_spin implementation that avoids unnecessary
cache/memory contention should be chosen for each arch, but for now,
the easiest thing is to perform a useless a_cas on the calling
thread's stack.
---
 arch/arm/atomic.h        | 1 +
 arch/microblaze/atomic.h | 1 +
 arch/mips/atomic.h       | 1 +
 arch/or1k/atomic.h       | 1 +
 arch/powerpc/atomic.h    | 1 +
 arch/sh/atomic.h         | 1 +
 6 files changed, 6 insertions(+)

diff --git a/arch/arm/atomic.h b/arch/arm/atomic.h
index 302e6d8f..52103542 100644
--- a/arch/arm/atomic.h
+++ b/arch/arm/atomic.h
@@ -103,6 +103,7 @@ static inline void a_store(volatile int *p, int x)
 
 static inline void a_spin()
 {
+	__k_cas(&(int){0}, 0, 0));
 }
 
 static inline void a_crash()
diff --git a/arch/microblaze/atomic.h b/arch/microblaze/atomic.h
index 96265fe6..abb79b53 100644
--- a/arch/microblaze/atomic.h
+++ b/arch/microblaze/atomic.h
@@ -97,6 +97,7 @@ static inline void a_store(volatile int *p, int x)
 
 static inline void a_spin()
 {
+	a_cas(&(int){0}, 0, 0);
 }
 
 static inline void a_crash()
diff --git a/arch/mips/atomic.h b/arch/mips/atomic.h
index 3ec03586..cc5bf498 100644
--- a/arch/mips/atomic.h
+++ b/arch/mips/atomic.h
@@ -137,6 +137,7 @@ static inline void a_store(volatile int *p, int x)
 
 static inline void a_spin()
 {
+	a_cas(&(int){0}, 0, 0);
 }
 
 static inline void a_crash()
diff --git a/arch/or1k/atomic.h b/arch/or1k/atomic.h
index 5b0411b0..f9e69815 100644
--- a/arch/or1k/atomic.h
+++ b/arch/or1k/atomic.h
@@ -74,6 +74,7 @@ static inline void a_store(volatile int *p, int x)
 
 static inline void a_spin()
 {
+	a_cas(&(int){0}, 0, 0);
 }
 
 static inline void a_crash()
diff --git a/arch/powerpc/atomic.h b/arch/powerpc/atomic.h
index 1044886d..1c50361e 100644
--- a/arch/powerpc/atomic.h
+++ b/arch/powerpc/atomic.h
@@ -80,6 +80,7 @@ static inline void a_store(volatile int *p, int x)
 
 static inline void a_spin()
 {
+	a_cas(&(int){0}, 0, 0);
 }
 
 static inline void a_crash()
diff --git a/arch/sh/atomic.h b/arch/sh/atomic.h
index 93ab54fe..b95bbffc 100644
--- a/arch/sh/atomic.h
+++ b/arch/sh/atomic.h
@@ -53,6 +53,7 @@ static inline void a_dec(volatile int *x)
 
 static inline void a_spin()
 {
+	a_cas(&(int){0}, 0, 0);
 }
 
 static inline void a_crash()