[PATCH v5 1/4] arch: Cleanup read_barrier_depends() and comments

Alexander Duyck
2014-11-19T01:26:00Z

This patch is meant to cleanup the handling of read_barrier_depends and
smp_read_barrier_depends. In multiple spots in the kernel headers
read_barrier_depends is defined as "do {} while (0)", however we then go
into the SMP vs non-SMP sections and have the SMP version reference
read_barrier_depends, and the non-SMP define it as yet another empty
do/while.

With this commit I went through and cleaned out the duplicate definitions
and reduced the number of definitions down to 2 per header. In addition I
moved the 50 line comments for the macro from the x86 and mips headers that
defined it as an empty do/while to those that were actually defining the
macro, alpha and blackfin.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
---
arch/alpha/include/asm/barrier.h | 51 ++++++++++++++++++++++++++++++
arch/blackfin/include/asm/barrier.h | 51 ++++++++++++++++++++++++++++++
arch/ia64/include/asm/barrier.h | 22 +++++--------
arch/metag/include/asm/barrier.h | 7 ++--
arch/mips/include/asm/barrier.h | 52 -------------------------------
arch/powerpc/include/asm/barrier.h | 6 ++--
arch/s390/include/asm/barrier.h | 5 ++-
arch/sparc/include/asm/barrier_64.h | 4 +-
arch/x86/include/asm/barrier.h | 59 ++---------------------------------
arch/x86/um/asm/barrier.h | 7 ++--
10 files changed, 129 insertions(+), 135 deletions(-)

diff --git a/arch/alpha/include/asm/barrier.h b/arch/alpha/include/asm/barrier.h
index 3832bdb..77516c8 100644
--- a/arch/alpha/include/asm/barrier.h
+++ b/arch/alpha/include/asm/barrier.h
@@ -7,6 +7,57 @@
#define rmb() __asm__ __volatile__("mb": : :"memory")
#define wmb() __asm__ __volatile__("wmb": : :"memory")

+/**
+ * read_barrier_depends - Flush all pending reads that subsequents reads
+ * depend on.
+ *
+ * No data-dependent reads from memory-like regions are ever reordered
+ * over this barrier. All reads preceding this primitive are guaranteed
+ * to access memory (but not necessarily other CPUs' caches) before any
+ * reads following this primitive that depend on the data return by
+ * any of the preceding reads. This primitive is much lighter weight than
+ * rmb() on most CPUs, and is never heavier weight than is
+ * rmb().
+ *
+ * These ordering constraints are respected by both the local CPU
+ * and the compiler.
+ *
+ * Ordering is not guaranteed by anything other than these primitives,
+ * not even by data dependencies. See the documentation for
+ * memory_barrier() for examples and URLs to more information.
+ *
+ * For example, the following code would force ordering (the initial
+ * value of "a" is zero, "b" is one, and "p" is "&a"):
+ *
+ * <programlisting>
+ * CPU 0 CPU 1
+ *
+ * b = 2;
+ * memory_barrier();
+ * p = &b; q = p;
+ * read_barrier_depends();
+ * d = *q;
+ * </programlisting>
+ *
+ * because the read of "*q" depends on the read of "p" and these
+ * two reads are separated by a read_barrier_depends(). However,
+ * the following code, with the same initial values for "a" and "b":
+ *
+ * <programlisting>
+ * CPU 0 CPU 1
+ *
+ * a = 2;
+ * memory_barrier();
+ * b = 3; y = b;
+ * read_barrier_depends();
+ * x = a;
+ * </programlisting>
+ *
+ * does not enforce ordering, since there is no data dependency between
+ * the read of "a" and the read of "b". Therefore, on some CPUs, such
+ * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
+ * in cases like this where there are no data dependencies.
+ */
#define read_barrier_depends() __asm__ __volatile__("mb": : :"memory")

#ifdef CONFIG_SMP
diff --git a/arch/blackfin/include/asm/barrier.h b/arch/blackfin/include/asm/barrier.h
index 4200068..dfb66fe 100644
--- a/arch/blackfin/include/asm/barrier.h
+++ b/arch/blackfin/include/asm/barrier.h
@@ -22,6 +22,57 @@
# define mb() do { barrier(); smp_check_barrier(); smp_mark_barrier(); } while (0)
# define rmb() do { barrier(); smp_check_barrier(); } while (0)
# define wmb() do { barrier(); smp_mark_barrier(); } while (0)
+/*
+ * read_barrier_depends - Flush all pending reads that subsequents reads
+ * depend on.
+ *
+ * No data-dependent reads from memory-like regions are ever reordered
+ * over this barrier. All reads preceding this primitive are guaranteed
+ * to access memory (but not necessarily other CPUs' caches) before any
+ * reads following this primitive that depend on the data return by
+ * any of the preceding reads. This primitive is much lighter weight than
+ * rmb() on most CPUs, and is never heavier weight than is
+ * rmb().
+ *
+ * These ordering constraints are respected by both the local CPU
+ * and the compiler.
+ *
+ * Ordering is not guaranteed by anything other than these primitives,
+ * not even by data dependencies. See the documentation for
+ * memory_barrier() for examples and URLs to more information.
+ *
+ * For example, the following code would force ordering (the initial
+ * value of "a" is zero, "b" is one, and "p" is "&a"):
+ *
+ * <programlisting>
+ * CPU 0 CPU 1
+ *
+ * b = 2;
+ * memory_barrier();
+ * p = &b; q = p;
+ * read_barrier_depends();
+ * d = *q;
+ * </programlisting>
+ *
+ * because the read of "*q" depends on the read of "p" and these
+ * two reads are separated by a read_barrier_depends(). However,
+ * the following code, with the same initial values for "a" and "b":
+ *
+ * <programlisting>
+ * CPU 0 CPU 1
+ *
+ * a = 2;
+ * memory_barrier();
+ * b = 3; y = b;
+ * read_barrier_depends();
+ * x = a;
+ * </programlisting>
+ *
+ * does not enforce ordering, since there is no data dependency between
+ * the read of "a" and the read of "b". Therefore, on some CPUs, such
+ * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
+ * in cases like this where there are no data dependencies.
+ */
# define read_barrier_depends() do { barrier(); smp_check_barrier(); } while (0)
#endif

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index a48957c..e8fffb0 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -35,26 +35,22 @@
* it's (presumably) much slower than mf and (b) mf.a is supported for
* sequential memory pages only.
*/
-#define mb() ia64_mf()
-#define rmb() mb()
-#define wmb() mb()
-#define read_barrier_depends() do { } while(0)
+#define mb() ia64_mf()
+#define rmb() mb()
+#define wmb() mb()

#ifdef CONFIG_SMP
# define smp_mb() mb()
-# define smp_rmb() rmb()
-# define smp_wmb() wmb()
-# define smp_read_barrier_depends() read_barrier_depends()
-
#else
-
# define smp_mb() barrier()
-# define smp_rmb() barrier()
-# define smp_wmb() barrier()
-# define smp_read_barrier_depends() do { } while(0)
-
#endif

+#define smp_rmb() smp_mb()
+#define smp_wmb() smp_mb()
+
+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)
+
#define smp_mb__before_atomic() barrier()
#define smp_mb__after_atomic() barrier()

diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h
index c7591e8..6d8b8c9 100644
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -47,8 +47,6 @@ static inline void wmb(void)
wr_fence();
}

-#define read_barrier_depends() do { } while (0)
-
#ifndef CONFIG_SMP
#define fence() do { } while (0)
#define smp_mb() barrier()
@@ -82,7 +80,10 @@ static inline void fence(void)
#define smp_wmb() barrier()
#endif
#endif
-#define smp_read_barrier_depends() do { } while (0)
+
+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)
+
#define set_mb(var, value) do { var = value; smp_mb(); } while (0)

#define smp_store_release(p, v) \
diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
index d0101dd..3d69aa8 100644
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -10,58 +10,6 @@

#include <asm/addrspace.h>

-/*
- * read_barrier_depends - Flush all pending reads that subsequents reads
- * depend on.
- *
- * No data-dependent reads from memory-like regions are ever reordered
- * over this barrier. All reads preceding this primitive are guaranteed
- * to access memory (but not necessarily other CPUs' caches) before any
- * reads following this primitive that depend on the data return by
- * any of the preceding reads. This primitive is much lighter weight than
- * rmb() on most CPUs, and is never heavier weight than is
- * rmb().
- *
- * These ordering constraints are respected by both the local CPU
- * and the compiler.
- *
- * Ordering is not guaranteed by anything other than these primitives,
- * not even by data dependencies. See the documentation for
- * memory_barrier() for examples and URLs to more information.
- *
- * For example, the following code would force ordering (the initial
- * value of "a" is zero, "b" is one, and "p" is "&a"):
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * b = 2;
- * memory_barrier();
- * p = &b; q = p;
- * read_barrier_depends();
- * d = *q;
- * </programlisting>
- *
- * because the read of "*q" depends on the read of "p" and these
- * two reads are separated by a read_barrier_depends(). However,
- * the following code, with the same initial values for "a" and "b":
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * a = 2;
- * memory_barrier();
- * b = 3; y = b;
- * read_barrier_depends();
- * x = a;
- * </programlisting>
- *
- * does not enforce ordering, since there is no data dependency between
- * the read of "a" and the read of "b". Therefore, on some CPUs, such
- * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
- * in cases like this where there are no data dependencies.
- */
-
#define read_barrier_depends() do { } while(0)
#define smp_read_barrier_depends() do { } while(0)

diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
index bab79a1..cb6d66c 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -33,7 +33,6 @@
#define mb() __asm__ __volatile__ ("sync" : : : "memory")
#define rmb() __asm__ __volatile__ ("sync" : : : "memory")
#define wmb() __asm__ __volatile__ ("sync" : : : "memory")
-#define read_barrier_depends() do { } while(0)

#define set_mb(var, value) do { var = value; mb(); } while (0)

@@ -50,16 +49,17 @@
#define smp_mb() mb()
#define smp_rmb() __lwsync()
#define smp_wmb() __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
-#define smp_read_barrier_depends() read_barrier_depends()
#else
#define __lwsync() barrier()

#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while(0)
#endif /* CONFIG_SMP */

+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)
+
/*
* This is a barrier which prevents following instructions from being
* started until the value of the argument x is known. For example, if
diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index b5dce65..33d191d 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -24,11 +24,12 @@

#define rmb() mb()
#define wmb() mb()
-#define read_barrier_depends() do { } while(0)
#define smp_mb() mb()
#define smp_rmb() rmb()
#define smp_wmb() wmb()
-#define smp_read_barrier_depends() read_barrier_depends()
+
+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)

#define smp_mb__before_atomic() smp_mb()
#define smp_mb__after_atomic() smp_mb()
diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h
index 305dcc3..6c974c0 100644
--- a/arch/sparc/include/asm/barrier_64.h
+++ b/arch/sparc/include/asm/barrier_64.h
@@ -37,7 +37,6 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
#define rmb() __asm__ __volatile__("":::"memory")
#define wmb() __asm__ __volatile__("":::"memory")

-#define read_barrier_depends() do { } while(0)
#define set_mb(__var, __value) \
do { __var = __value; membar_safe("#StoreLoad"); } while(0)

@@ -51,7 +50,8 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
#define smp_wmb() __asm__ __volatile__("":::"memory")
#endif

-#define smp_read_barrier_depends() do { } while(0)
+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)

#define smp_store_release(p, v) \
do { \
diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index 0f4460b..5238000 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -24,60 +24,6 @@
#define wmb() asm volatile("sfence" ::: "memory")
#endif

-/**
- * read_barrier_depends - Flush all pending reads that subsequents reads
- * depend on.
- *
- * No data-dependent reads from memory-like regions are ever reordered
- * over this barrier. All reads preceding this primitive are guaranteed
- * to access memory (but not necessarily other CPUs' caches) before any
- * reads following this primitive that depend on the data return by
- * any of the preceding reads. This primitive is much lighter weight than
- * rmb() on most CPUs, and is never heavier weight than is
- * rmb().
- *
- * These ordering constraints are respected by both the local CPU
- * and the compiler.
- *
- * Ordering is not guaranteed by anything other than these primitives,
- * not even by data dependencies. See the documentation for
- * memory_barrier() for examples and URLs to more information.
- *
- * For example, the following code would force ordering (the initial
- * value of "a" is zero, "b" is one, and "p" is "&a"):
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * b = 2;
- * memory_barrier();
- * p = &b; q = p;
- * read_barrier_depends();
- * d = *q;
- * </programlisting>
- *
- * because the read of "*q" depends on the read of "p" and these
- * two reads are separated by a read_barrier_depends(). However,
- * the following code, with the same initial values for "a" and "b":
- *
- * <programlisting>
- * CPU 0 CPU 1
- *
- * a = 2;
- * memory_barrier();
- * b = 3; y = b;
- * read_barrier_depends();
- * x = a;
- * </programlisting>
- *
- * does not enforce ordering, since there is no data dependency between
- * the read of "a" and the read of "b". Therefore, on some CPUs, such
- * as Alpha, "y" could be set to 3 and "x" to 0. Use rmb()
- * in cases like this where there are no data dependencies.
- **/
-
-#define read_barrier_depends() do { } while (0)
-
#ifdef CONFIG_SMP
#define smp_mb() mb()
#ifdef CONFIG_X86_PPRO_FENCE
@@ -86,16 +32,17 @@
# define smp_rmb() barrier()
#endif
#define smp_wmb() barrier()
-#define smp_read_barrier_depends() read_barrier_depends()
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)
#else /* !SMP */
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while (0)
#define set_mb(var, value) do { var = value; barrier(); } while (0)
#endif /* SMP */

+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)
+
#if defined(CONFIG_X86_PPRO_FENCE)

/*
diff --git a/arch/x86/um/asm/barrier.h b/arch/x86/um/asm/barrier.h
index cc04e67..d6511d9 100644
--- a/arch/x86/um/asm/barrier.h
+++ b/arch/x86/um/asm/barrier.h
@@ -29,8 +29,6 @@

#endif /* CONFIG_X86_32 */

-#define read_barrier_depends() do { } while (0)
-
#ifdef CONFIG_SMP

#define smp_mb() mb()
@@ -42,7 +40,6 @@

#define smp_wmb() barrier()

-#define smp_read_barrier_depends() read_barrier_depends()
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)

#else /* CONFIG_SMP */
@@ -50,11 +47,13 @@
#define smp_mb() barrier()
#define smp_rmb() barrier()
#define smp_wmb() barrier()
-#define smp_read_barrier_depends() do { } while (0)
#define set_mb(var, value) do { var = value; barrier(); } while (0)

#endif /* CONFIG_SMP */

+#define read_barrier_depends() do { } while (0)
+#define smp_read_barrier_depends() do { } while (0)
+
/*
* Stop RDTSC speculation. This is needed when you need to use RDTSC
* (or get_cycles or vread that possibly accesses the TSC) in a defined