[PATCH 0/3] Remove lockless_dereference

[PATCH 0/3] Remove lockless_dereference

[Will Deacon]

Hi all,

These patches remove lockless_dereference from the kernel. It's only used
in a handful of places relative to READ_ONCE and ACCESS_ONCE and is only
required for correctness on Alpha. Consequently, READ_ONCE is strengthened
on Alpha systems to include the smp_read_barrier_depends implicitly and
Alpha's release and release atomic_t and atomic64_t operations are also
upgraded.

The nastiest part about all of this was actually fixing the circular
includes of compiler.h, which is an existing problem that doesn't crop
up in practice because lockless_dereference is rarely used.

Thanks,

Will

--->8

Will Deacon (3):
  linux/compiler.h: Split into compiler.h and compiler-types.h
  locking/barriers: Kill lockless_dereference
  alpha: atomics: Add smp_read_barrier_depends() to release/relaxed
    atomics

 Documentation/memory-barriers.txt                  |  12 -
 .../translations/ko_KR/memory-barriers.txt         |  12 -
 arch/alpha/include/asm/atomic.h                    |  13 +
 arch/arm/include/asm/ptrace.h                      |   3 +-
 arch/x86/events/core.c                             |   2 +-
 arch/x86/include/asm/mmu_context.h                 |   4 +-
 arch/x86/kernel/ldt.c                              |   2 +-
 drivers/md/dm-mpath.c                              |  20 +-
 fs/dcache.c                                        |   4 +-
 fs/overlayfs/ovl_entry.h                           |   2 +-
 fs/overlayfs/readdir.c                             |   2 +-
 include/linux/compiler-clang.h                     |   2 +-
 include/linux/compiler-gcc.h                       |   2 +-
 include/linux/compiler-intel.h                     |   2 +-
 include/linux/compiler-types.h                     | 274 ++++++++++++++++++++
 include/linux/compiler.h                           | 286 +--------------------
 include/linux/linkage.h                            |   2 +-
 include/linux/rculist.h                            |   4 +-
 include/linux/rcupdate.h                           |   4 +-
 include/uapi/linux/stddef.h                        |   2 +-
 kernel/events/core.c                               |   4 +-
 kernel/seccomp.c                                   |   2 +-
 kernel/task_work.c                                 |   2 +-
 mm/slab.h                                          |   2 +-
 scripts/headers_install.sh                         |   2 +-
 25 files changed, 325 insertions(+), 341 deletions(-)
 create mode 100644 include/linux/compiler-types.h

-- 
2.1.4

[PATCH 1/3] linux/compiler.h: Split into compiler.h and compiler-types.h

[Will Deacon]

linux/compiler.h is included indirectly by linux/types.h via
uapi/linux/types.h -> uapi/linux/posix_types.h -> linux/stddef.h
-> uapi/linux/stddef.h and is needed to provide a proper definition of
offsetof.

Unfortunately, compiler.h requires a definition of
smp_read_barrier_depends() for defining lockless_dereference and soon
for defining READ_ONCE, which means that all
users of READ_ONCE will need to include asm/barrier.h to avoid splats
such as:

   In file included from include/uapi/linux/stddef.h:1:0,
                    from include/linux/stddef.h:4,
                    from arch/h8300/kernel/asm-offsets.c:11:
   include/linux/list.h: In function 'list_empty':
>> include/linux/compiler.h:343:2: error: implicit declaration of function 'smp_read_barrier_depends' [-Werror=implicit-function-declaration]
     smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
     ^

A better alternative is to include asm/barrier.h in linux/compiler.h,
but this requires a type definition for "bool" on some architectures
(e.g. x86), which is defined later by linux/types.h. Type "bool" is also
used directly in linux/compiler.h, so the whole thing is pretty fragile.

This patch splits compiler.h in two: compiler-types.h contains type
annotations, definitions and the compiler-specific parts, whereas
compiler.h #includes compiler-types.h and additionally defines macros
such as {READ,WRITE.ACCESS}_ONCE.

uapi/linux/stddef.h and linux/linkage.h are then moved over to include
linux/compiler-types.h, which fixes the build for h8 and blackfin.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/arm/include/asm/ptrace.h  |   3 +-
 include/linux/compiler-clang.h |   2 +-
 include/linux/compiler-gcc.h   |   2 +-
 include/linux/compiler-intel.h |   2 +-
 include/linux/compiler-types.h | 274 +++++++++++++++++++++++++++++++++++++++++
 include/linux/compiler.h       | 265 +--------------------------------------
 include/linux/linkage.h        |   2 +-
 include/uapi/linux/stddef.h    |   2 +-
 scripts/headers_install.sh     |   2 +-
 9 files changed, 284 insertions(+), 270 deletions(-)
 create mode 100644 include/linux/compiler-types.h

diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index e9c9a117bd25..c7cdbb43ae7c 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -126,8 +126,7 @@ extern unsigned long profile_pc(struct pt_regs *regs);
 /*
  * kprobe-based event tracer support
  */
-#include <linux/stddef.h>
-#include <linux/types.h>
+#include <linux/compiler.h>
 #define MAX_REG_OFFSET (offsetof(struct pt_regs, ARM_ORIG_r0))
 
 extern int regs_query_register_offset(const char *name);
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index de179993e039..5947a3e6c0e6 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -1,4 +1,4 @@
-#ifndef __LINUX_COMPILER_H
+#ifndef __LINUX_COMPILER_TYPES_H
 #error "Please don't include <linux/compiler-clang.h> directly, include <linux/compiler.h> instead."
 #endif
 
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 16d41de92ee3..ce8e965646ef 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -1,4 +1,4 @@
-#ifndef __LINUX_COMPILER_H
+#ifndef __LINUX_COMPILER_TYPES_H
 #error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
 #endif
 
diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index d4c71132d07f..e438ac89c692 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -1,4 +1,4 @@
-#ifndef __LINUX_COMPILER_H
+#ifndef __LINUX_COMPILER_TYPES_H
 #error "Please don't include <linux/compiler-intel.h> directly, include <linux/compiler.h> instead."
 #endif
 
diff --git a/include/linux/compiler-types.h b/include/linux/compiler-types.h
new file mode 100644
index 000000000000..6b79a9bba9a7
--- /dev/null
+++ b/include/linux/compiler-types.h
@@ -0,0 +1,274 @@
+#ifndef __LINUX_COMPILER_TYPES_H
+#define __LINUX_COMPILER_TYPES_H
+
+#ifndef __ASSEMBLY__
+
+#ifdef __CHECKER__
+# define __user		__attribute__((noderef, address_space(1)))
+# define __kernel	__attribute__((address_space(0)))
+# define __safe		__attribute__((safe))
+# define __force	__attribute__((force))
+# define __nocast	__attribute__((nocast))
+# define __iomem	__attribute__((noderef, address_space(2)))
+# define __must_hold(x)	__attribute__((context(x,1,1)))
+# define __acquires(x)	__attribute__((context(x,0,1)))
+# define __releases(x)	__attribute__((context(x,1,0)))
+# define __acquire(x)	__context__(x,1)
+# define __release(x)	__context__(x,-1)
+# define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
+# define __percpu	__attribute__((noderef, address_space(3)))
+# define __rcu		__attribute__((noderef, address_space(4)))
+# define __private	__attribute__((noderef))
+extern void __chk_user_ptr(const volatile void __user *);
+extern void __chk_io_ptr(const volatile void __iomem *);
+# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
+#else /* __CHECKER__ */
+# ifdef STRUCTLEAK_PLUGIN
+#  define __user __attribute__((user))
+# else
+#  define __user
+# endif
+# define __kernel
+# define __safe
+# define __force
+# define __nocast
+# define __iomem
+# define __chk_user_ptr(x) (void)0
+# define __chk_io_ptr(x) (void)0
+# define __builtin_warning(x, y...) (1)
+# define __must_hold(x)
+# define __acquires(x)
+# define __releases(x)
+# define __acquire(x) (void)0
+# define __release(x) (void)0
+# define __cond_lock(x,c) (c)
+# define __percpu
+# define __rcu
+# define __private
+# define ACCESS_PRIVATE(p, member) ((p)->member)
+#endif /* __CHECKER__ */
+
+/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
+#define ___PASTE(a,b) a##b
+#define __PASTE(a,b) ___PASTE(a,b)
+
+#ifdef __KERNEL__
+
+#ifdef __GNUC__
+#include <linux/compiler-gcc.h>
+#endif
+
+#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__)
+#define notrace __attribute__((hotpatch(0,0)))
+#else
+#define notrace __attribute__((no_instrument_function))
+#endif
+
+/* Intel compiler defines __GNUC__. So we will overwrite implementations
+ * coming from above header files here
+ */
+#ifdef __INTEL_COMPILER
+# include <linux/compiler-intel.h>
+#endif
+
+/* Clang compiler defines __GNUC__. So we will overwrite implementations
+ * coming from above header files here
+ */
+#ifdef __clang__
+#include <linux/compiler-clang.h>
+#endif
+
+/*
+ * Generic compiler-dependent macros required for kernel
+ * build go below this comment. Actual compiler/compiler version
+ * specific implementations come from the above header files
+ */
+
+struct ftrace_branch_data {
+	const char *func;
+	const char *file;
+	unsigned line;
+	union {
+		struct {
+			unsigned long correct;
+			unsigned long incorrect;
+		};
+		struct {
+			unsigned long miss;
+			unsigned long hit;
+		};
+		unsigned long miss_hit[2];
+	};
+};
+
+struct ftrace_likely_data {
+	struct ftrace_branch_data	data;
+	unsigned long			constant;
+};
+
+#endif /* __KERNEL__ */
+
+#endif /* __ASSEMBLY__ */
+
+#ifdef __KERNEL__
+/*
+ * Allow us to mark functions as 'deprecated' and have gcc emit a nice
+ * warning for each use, in hopes of speeding the functions removal.
+ * Usage is:
+ * 		int __deprecated foo(void)
+ */
+#ifndef __deprecated
+# define __deprecated		/* unimplemented */
+#endif
+
+#ifdef MODULE
+#define __deprecated_for_modules __deprecated
+#else
+#define __deprecated_for_modules
+#endif
+
+#ifndef __must_check
+#define __must_check
+#endif
+
+#ifndef CONFIG_ENABLE_MUST_CHECK
+#undef __must_check
+#define __must_check
+#endif
+#ifndef CONFIG_ENABLE_WARN_DEPRECATED
+#undef __deprecated
+#undef __deprecated_for_modules
+#define __deprecated
+#define __deprecated_for_modules
+#endif
+
+#ifndef __malloc
+#define __malloc
+#endif
+
+/*
+ * Allow us to avoid 'defined but not used' warnings on functions and data,
+ * as well as force them to be emitted to the assembly file.
+ *
+ * As of gcc 3.4, static functions that are not marked with attribute((used))
+ * may be elided from the assembly file.  As of gcc 3.4, static data not so
+ * marked will not be elided, but this may change in a future gcc version.
+ *
+ * NOTE: Because distributions shipped with a backported unit-at-a-time
+ * compiler in gcc 3.3, we must define __used to be __attribute__((used))
+ * for gcc >=3.3 instead of 3.4.
+ *
+ * In prior versions of gcc, such functions and data would be emitted, but
+ * would be warned about except with attribute((unused)).
+ *
+ * Mark functions that are referenced only in inline assembly as __used so
+ * the code is emitted even though it appears to be unreferenced.
+ */
+#ifndef __used
+# define __used			/* unimplemented */
+#endif
+
+#ifndef __maybe_unused
+# define __maybe_unused		/* unimplemented */
+#endif
+
+#ifndef __always_unused
+# define __always_unused	/* unimplemented */
+#endif
+
+#ifndef noinline
+#define noinline
+#endif
+
+/*
+ * Rather then using noinline to prevent stack consumption, use
+ * noinline_for_stack instead.  For documentation reasons.
+ */
+#define noinline_for_stack noinline
+
+#ifndef __always_inline
+#define __always_inline inline
+#endif
+
+#endif /* __KERNEL__ */
+
+/*
+ * From the GCC manual:
+ *
+ * Many functions do not examine any values except their arguments,
+ * and have no effects except the return value.  Basically this is
+ * just slightly more strict class than the `pure' attribute above,
+ * since function is not allowed to read global memory.
+ *
+ * Note that a function that has pointer arguments and examines the
+ * data pointed to must _not_ be declared `const'.  Likewise, a
+ * function that calls a non-`const' function usually must not be
+ * `const'.  It does not make sense for a `const' function to return
+ * `void'.
+ */
+#ifndef __attribute_const__
+# define __attribute_const__	/* unimplemented */
+#endif
+
+#ifndef __designated_init
+# define __designated_init
+#endif
+
+#ifndef __latent_entropy
+# define __latent_entropy
+#endif
+
+#ifndef __randomize_layout
+# define __randomize_layout __designated_init
+#endif
+
+#ifndef __no_randomize_layout
+# define __no_randomize_layout
+#endif
+
+#ifndef randomized_struct_fields_start
+# define randomized_struct_fields_start
+# define randomized_struct_fields_end
+#endif
+
+/*
+ * Tell gcc if a function is cold. The compiler will assume any path
+ * directly leading to the call is unlikely.
+ */
+
+#ifndef __cold
+#define __cold
+#endif
+
+/* Simple shorthand for a section definition */
+#ifndef __section
+# define __section(S) __attribute__ ((__section__(#S)))
+#endif
+
+#ifndef __visible
+#define __visible
+#endif
+
+#ifndef __nostackprotector
+# define __nostackprotector
+#endif
+
+/*
+ * Assume alignment of return value.
+ */
+#ifndef __assume_aligned
+#define __assume_aligned(a, ...)
+#endif
+
+
+/* Are two types/vars the same type (ignoring qualifiers)? */
+#ifndef __same_type
+# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
+#endif
+
+/* Is this type a native word size -- useful for atomic operations */
+#ifndef __native_word
+# define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
+#endif
+
+#endif /* __LINUX_COMPILER_TYPES_H */
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index e95a2631e545..c714239f453f 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -1,111 +1,12 @@
 #ifndef __LINUX_COMPILER_H
 #define __LINUX_COMPILER_H
 
-#ifndef __ASSEMBLY__
+#include <linux/compiler-types.h>
 
-#ifdef __CHECKER__
-# define __user		__attribute__((noderef, address_space(1)))
-# define __kernel	__attribute__((address_space(0)))
-# define __safe		__attribute__((safe))
-# define __force	__attribute__((force))
-# define __nocast	__attribute__((nocast))
-# define __iomem	__attribute__((noderef, address_space(2)))
-# define __must_hold(x)	__attribute__((context(x,1,1)))
-# define __acquires(x)	__attribute__((context(x,0,1)))
-# define __releases(x)	__attribute__((context(x,1,0)))
-# define __acquire(x)	__context__(x,1)
-# define __release(x)	__context__(x,-1)
-# define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
-# define __percpu	__attribute__((noderef, address_space(3)))
-# define __rcu		__attribute__((noderef, address_space(4)))
-# define __private	__attribute__((noderef))
-extern void __chk_user_ptr(const volatile void __user *);
-extern void __chk_io_ptr(const volatile void __iomem *);
-# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
-#else /* __CHECKER__ */
-# ifdef STRUCTLEAK_PLUGIN
-#  define __user __attribute__((user))
-# else
-#  define __user
-# endif
-# define __kernel
-# define __safe
-# define __force
-# define __nocast
-# define __iomem
-# define __chk_user_ptr(x) (void)0
-# define __chk_io_ptr(x) (void)0
-# define __builtin_warning(x, y...) (1)
-# define __must_hold(x)
-# define __acquires(x)
-# define __releases(x)
-# define __acquire(x) (void)0
-# define __release(x) (void)0
-# define __cond_lock(x,c) (c)
-# define __percpu
-# define __rcu
-# define __private
-# define ACCESS_PRIVATE(p, member) ((p)->member)
-#endif /* __CHECKER__ */
-
-/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
-#define ___PASTE(a,b) a##b
-#define __PASTE(a,b) ___PASTE(a,b)
+#ifndef __ASSEMBLY__
 
 #ifdef __KERNEL__
 
-#ifdef __GNUC__
-#include <linux/compiler-gcc.h>
-#endif
-
-#if defined(CC_USING_HOTPATCH) && !defined(__CHECKER__)
-#define notrace __attribute__((hotpatch(0,0)))
-#else
-#define notrace __attribute__((no_instrument_function))
-#endif
-
-/* Intel compiler defines __GNUC__. So we will overwrite implementations
- * coming from above header files here
- */
-#ifdef __INTEL_COMPILER
-# include <linux/compiler-intel.h>
-#endif
-
-/* Clang compiler defines __GNUC__. So we will overwrite implementations
- * coming from above header files here
- */
-#ifdef __clang__
-#include <linux/compiler-clang.h>
-#endif
-
-/*
- * Generic compiler-dependent macros required for kernel
- * build go below this comment. Actual compiler/compiler version
- * specific implementations come from the above header files
- */
-
-struct ftrace_branch_data {
-	const char *func;
-	const char *file;
-	unsigned line;
-	union {
-		struct {
-			unsigned long correct;
-			unsigned long incorrect;
-		};
-		struct {
-			unsigned long miss;
-			unsigned long hit;
-		};
-		unsigned long miss_hit[2];
-	};
-};
-
-struct ftrace_likely_data {
-	struct ftrace_branch_data	data;
-	unsigned long			constant;
-};
-
 /*
  * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
  * to disable branch tracing on a per file basis.
@@ -332,6 +233,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
  * with an explicit memory barrier or atomic instruction that provides the
  * required ordering.
  */
+#include <asm/barrier.h>
 
 #define __READ_ONCE(x, check)						\
 ({									\
@@ -362,167 +264,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 
 #endif /* __ASSEMBLY__ */
 
-#ifdef __KERNEL__
-/*
- * Allow us to mark functions as 'deprecated' and have gcc emit a nice
- * warning for each use, in hopes of speeding the functions removal.
- * Usage is:
- * 		int __deprecated foo(void)
- */
-#ifndef __deprecated
-# define __deprecated		/* unimplemented */
-#endif
-
-#ifdef MODULE
-#define __deprecated_for_modules __deprecated
-#else
-#define __deprecated_for_modules
-#endif
-
-#ifndef __must_check
-#define __must_check
-#endif
-
-#ifndef CONFIG_ENABLE_MUST_CHECK
-#undef __must_check
-#define __must_check
-#endif
-#ifndef CONFIG_ENABLE_WARN_DEPRECATED
-#undef __deprecated
-#undef __deprecated_for_modules
-#define __deprecated
-#define __deprecated_for_modules
-#endif
-
-#ifndef __malloc
-#define __malloc
-#endif
-
-/*
- * Allow us to avoid 'defined but not used' warnings on functions and data,
- * as well as force them to be emitted to the assembly file.
- *
- * As of gcc 3.4, static functions that are not marked with attribute((used))
- * may be elided from the assembly file.  As of gcc 3.4, static data not so
- * marked will not be elided, but this may change in a future gcc version.
- *
- * NOTE: Because distributions shipped with a backported unit-at-a-time
- * compiler in gcc 3.3, we must define __used to be __attribute__((used))
- * for gcc >=3.3 instead of 3.4.
- *
- * In prior versions of gcc, such functions and data would be emitted, but
- * would be warned about except with attribute((unused)).
- *
- * Mark functions that are referenced only in inline assembly as __used so
- * the code is emitted even though it appears to be unreferenced.
- */
-#ifndef __used
-# define __used			/* unimplemented */
-#endif
-
-#ifndef __maybe_unused
-# define __maybe_unused		/* unimplemented */
-#endif
-
-#ifndef __always_unused
-# define __always_unused	/* unimplemented */
-#endif
-
-#ifndef noinline
-#define noinline
-#endif
-
-/*
- * Rather then using noinline to prevent stack consumption, use
- * noinline_for_stack instead.  For documentation reasons.
- */
-#define noinline_for_stack noinline
-
-#ifndef __always_inline
-#define __always_inline inline
-#endif
-
-#endif /* __KERNEL__ */
-
-/*
- * From the GCC manual:
- *
- * Many functions do not examine any values except their arguments,
- * and have no effects except the return value.  Basically this is
- * just slightly more strict class than the `pure' attribute above,
- * since function is not allowed to read global memory.
- *
- * Note that a function that has pointer arguments and examines the
- * data pointed to must _not_ be declared `const'.  Likewise, a
- * function that calls a non-`const' function usually must not be
- * `const'.  It does not make sense for a `const' function to return
- * `void'.
- */
-#ifndef __attribute_const__
-# define __attribute_const__	/* unimplemented */
-#endif
-
-#ifndef __designated_init
-# define __designated_init
-#endif
-
-#ifndef __latent_entropy
-# define __latent_entropy
-#endif
-
-#ifndef __randomize_layout
-# define __randomize_layout __designated_init
-#endif
-
-#ifndef __no_randomize_layout
-# define __no_randomize_layout
-#endif
-
-#ifndef randomized_struct_fields_start
-# define randomized_struct_fields_start
-# define randomized_struct_fields_end
-#endif
-
-/*
- * Tell gcc if a function is cold. The compiler will assume any path
- * directly leading to the call is unlikely.
- */
-
-#ifndef __cold
-#define __cold
-#endif
-
-/* Simple shorthand for a section definition */
-#ifndef __section
-# define __section(S) __attribute__ ((__section__(#S)))
-#endif
-
-#ifndef __visible
-#define __visible
-#endif
-
-#ifndef __nostackprotector
-# define __nostackprotector
-#endif
-
-/*
- * Assume alignment of return value.
- */
-#ifndef __assume_aligned
-#define __assume_aligned(a, ...)
-#endif
-
-
-/* Are two types/vars the same type (ignoring qualifiers)? */
-#ifndef __same_type
-# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
-#endif
-
-/* Is this type a native word size -- useful for atomic operations */
-#ifndef __native_word
-# define __native_word(t) (sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
-#endif
-
 /* Compile time object size, -1 for unknown */
 #ifndef __compiletime_object_size
 # define __compiletime_object_size(obj) -1
diff --git a/include/linux/linkage.h b/include/linux/linkage.h
index a6a42dd02466..9599d13cea0c 100644
--- a/include/linux/linkage.h
+++ b/include/linux/linkage.h
@@ -1,7 +1,7 @@
 #ifndef _LINUX_LINKAGE_H
 #define _LINUX_LINKAGE_H
 
-#include <linux/compiler.h>
+#include <linux/compiler-types.h>
 #include <linux/stringify.h>
 #include <linux/export.h>
 #include <asm/linkage.h>
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 621fa8ac4425..1ec6a7867c46 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -1,4 +1,4 @@
-#include <linux/compiler.h>
+#include <linux/compiler-types.h>
 
 #ifndef __always_inline
 #define __always_inline inline
diff --git a/scripts/headers_install.sh b/scripts/headers_install.sh
index fdebd66f8fc1..bbb7f3d35289 100755
--- a/scripts/headers_install.sh
+++ b/scripts/headers_install.sh
@@ -33,7 +33,7 @@ do
 	sed -r \
 		-e 's/([ \t(])(__user|__force|__iomem)[ \t]/\1/g' \
 		-e 's/__attribute_const__([ \t]|$)/\1/g' \
-		-e 's@^#include <linux/compiler.h>@@' \
+		-e 's@^#include <linux/compiler(|-types).h>@@' \
 		-e 's/(^|[^a-zA-Z0-9])__packed([^a-zA-Z0-9_]|$)/\1__attribute__((packed))\2/g' \
 		-e 's/(^|[ \t(])(inline|asm|volatile)([ \t(]|$)/\1__\2__\3/g' \
 		-e 's@#(ifndef|define|endif[ \t]*/[*])[ \t]*_UAPI@#\1 @' \
-- 
2.1.4

[PATCH 2/3] locking/barriers: Kill lockless_dereference

[Will Deacon]

lockless_dereference is a nice idea, but its gained little traction in
kernel code since it's introduction three years ago. This is partly
because it's a pain to type, but also because using READ_ONCE instead
will work correctly on all architectures apart from Alpha, which is a
fully supported but somewhat niche architecture these days.

This patch moves smp_read_barrier_depends() (a NOP on all architectures
other than Alpha) from lockless_dereference into READ_ONCE, converts
the few actual users over to READ_ONCE and then finally removes
lockless_dereference altogether.

Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 Documentation/memory-barriers.txt                   | 12 ------------
 .../translations/ko_KR/memory-barriers.txt          | 12 ------------
 arch/x86/events/core.c                              |  2 +-
 arch/x86/include/asm/mmu_context.h                  |  4 ++--
 arch/x86/kernel/ldt.c                               |  2 +-
 drivers/md/dm-mpath.c                               | 20 ++++++++++----------
 fs/dcache.c                                         |  4 ++--
 fs/overlayfs/ovl_entry.h                            |  2 +-
 fs/overlayfs/readdir.c                              |  2 +-
 include/linux/compiler.h                            | 21 +--------------------
 include/linux/rculist.h                             |  4 ++--
 include/linux/rcupdate.h                            |  4 ++--
 kernel/events/core.c                                |  4 ++--
 kernel/seccomp.c                                    |  2 +-
 kernel/task_work.c                                  |  2 +-
 mm/slab.h                                           |  2 +-
 16 files changed, 28 insertions(+), 71 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index b759a60624fd..470a682f3fa4 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1886,18 +1886,6 @@ There are some more advanced barrier functions:
      See Documentation/atomic_{t,bitops}.txt for more information.
 
 
- (*) lockless_dereference();
-
-     This can be thought of as a pointer-fetch wrapper around the
-     smp_read_barrier_depends() data-dependency barrier.
-
-     This is also similar to rcu_dereference(), but in cases where
-     object lifetime is handled by some mechanism other than RCU, for
-     example, when the objects removed only when the system goes down.
-     In addition, lockless_dereference() is used in some data structures
-     that can be used both with and without RCU.
-
-
  (*) dma_wmb();
  (*) dma_rmb();
 
diff --git a/Documentation/translations/ko_KR/memory-barriers.txt b/Documentation/translations/ko_KR/memory-barriers.txt
index a7a813258013..ec3b46e27b7a 100644
--- a/Documentation/translations/ko_KR/memory-barriers.txt
+++ b/Documentation/translations/ko_KR/memory-barriers.txt
@@ -1858,18 +1858,6 @@ Mandatory 배리어들은 SMP 시스템에서도 UP 시스템에서도 SMP 효
      참고하세요.
 
 
- (*) lockless_dereference();
-
-     이 함수는 smp_read_barrier_depends() 데이터 의존성 배리어를 사용하는
-     포인터 읽어오기 래퍼(wrapper) 함수로 생각될 수 있습니다.
-
-     객체의 라이프타임이 RCU 외의 메커니즘으로 관리된다는 점을 제외하면
-     rcu_dereference() 와도 유사한데, 예를 들면 객체가 시스템이 꺼질 때에만
-     제거되는 경우 등입니다.  또한, lockless_dereference() 은 RCU 와 함께
-     사용될수도, RCU 없이 사용될 수도 있는 일부 데이터 구조에 사용되고
-     있습니다.
-
-
  (*) dma_wmb();
  (*) dma_rmb();
 
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 80534d3c2480..589af1eec7c1 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2371,7 +2371,7 @@ static unsigned long get_segment_base(unsigned int segment)
 		struct ldt_struct *ldt;
 
 		/* IRQs are off, so this synchronizes with smp_store_release */
-		ldt = lockless_dereference(current->active_mm->context.ldt);
+		ldt = READ_ONCE(current->active_mm->context.ldt);
 		if (!ldt || idx >= ldt->nr_entries)
 			return 0;
 
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index c120b5db178a..9037a4e546e8 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -72,8 +72,8 @@ static inline void load_mm_ldt(struct mm_struct *mm)
 #ifdef CONFIG_MODIFY_LDT_SYSCALL
 	struct ldt_struct *ldt;
 
-	/* lockless_dereference synchronizes with smp_store_release */
-	ldt = lockless_dereference(mm->context.ldt);
+	/* READ_ONCE synchronizes with smp_store_release */
+	ldt = READ_ONCE(mm->context.ldt);
 
 	/*
 	 * Any change to mm->context.ldt is followed by an IPI to all
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index f0e64db18ac8..0a21390642c4 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -101,7 +101,7 @@ static void finalize_ldt_struct(struct ldt_struct *ldt)
 static void install_ldt(struct mm_struct *current_mm,
 			struct ldt_struct *ldt)
 {
-	/* Synchronizes with lockless_dereference in load_mm_ldt. */
+	/* Synchronizes with READ_ONCE in load_mm_ldt. */
 	smp_store_release(&current_mm->context.ldt, ldt);
 
 	/* Activate the LDT for all CPUs using current_mm. */
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 11f273d2f018..3f88c9d32f7e 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -366,7 +366,7 @@ static struct pgpath *choose_path_in_pg(struct multipath *m,
 
 	pgpath = path_to_pgpath(path);
 
-	if (unlikely(lockless_dereference(m->current_pg) != pg)) {
+	if (unlikely(READ_ONCE(m->current_pg) != pg)) {
 		/* Only update current_pgpath if pg changed */
 		spin_lock_irqsave(&m->lock, flags);
 		m->current_pgpath = pgpath;
@@ -390,7 +390,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
 	}
 
 	/* Were we instructed to switch PG? */
-	if (lockless_dereference(m->next_pg)) {
+	if (READ_ONCE(m->next_pg)) {
 		spin_lock_irqsave(&m->lock, flags);
 		pg = m->next_pg;
 		if (!pg) {
@@ -406,7 +406,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
 
 	/* Don't change PG until it has no remaining paths */
 check_current_pg:
-	pg = lockless_dereference(m->current_pg);
+	pg = READ_ONCE(m->current_pg);
 	if (pg) {
 		pgpath = choose_path_in_pg(m, pg, nr_bytes);
 		if (!IS_ERR_OR_NULL(pgpath))
@@ -473,7 +473,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
 	struct request *clone;
 
 	/* Do we need to select a new pgpath? */
-	pgpath = lockless_dereference(m->current_pgpath);
+	pgpath = READ_ONCE(m->current_pgpath);
 	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))
 		pgpath = choose_pgpath(m, nr_bytes);
 
@@ -535,7 +535,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
 	bool queue_io;
 
 	/* Do we need to select a new pgpath? */
-	pgpath = lockless_dereference(m->current_pgpath);
+	pgpath = READ_ONCE(m->current_pgpath);
 	queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
 	if (!pgpath || !queue_io)
 		pgpath = choose_pgpath(m, nr_bytes);
@@ -1804,7 +1804,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
 	struct pgpath *current_pgpath;
 	int r;
 
-	current_pgpath = lockless_dereference(m->current_pgpath);
+	current_pgpath = READ_ONCE(m->current_pgpath);
 	if (!current_pgpath)
 		current_pgpath = choose_pgpath(m, 0);
 
@@ -1826,7 +1826,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
 	}
 
 	if (r == -ENOTCONN) {
-		if (!lockless_dereference(m->current_pg)) {
+		if (!READ_ONCE(m->current_pg)) {
 			/* Path status changed, redo selection */
 			(void) choose_pgpath(m, 0);
 		}
@@ -1895,9 +1895,9 @@ static int multipath_busy(struct dm_target *ti)
 		return (m->queue_mode != DM_TYPE_MQ_REQUEST_BASED);
 
 	/* Guess which priority_group will be used at next mapping time */
-	pg = lockless_dereference(m->current_pg);
-	next_pg = lockless_dereference(m->next_pg);
-	if (unlikely(!lockless_dereference(m->current_pgpath) && next_pg))
+	pg = READ_ONCE(m->current_pg);
+	next_pg = READ_ONCE(m->next_pg);
+	if (unlikely(!READ_ONCE(m->current_pgpath) && next_pg))
 		pg = next_pg;
 
 	if (!pg) {
diff --git a/fs/dcache.c b/fs/dcache.c
index f90141387f01..34c852af215c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -231,7 +231,7 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
 {
 	/*
 	 * Be careful about RCU walk racing with rename:
-	 * use 'lockless_dereference' to fetch the name pointer.
+	 * use 'READ_ONCE' to fetch the name pointer.
 	 *
 	 * NOTE! Even if a rename will mean that the length
 	 * was not loaded atomically, we don't care. The
@@ -245,7 +245,7 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
 	 * early because the data cannot match (there can
 	 * be no NUL in the ct/tcount data)
 	 */
-	const unsigned char *cs = lockless_dereference(dentry->d_name.name);
+	const unsigned char *cs = READ_ONCE(dentry->d_name.name);
 
 	return dentry_string_cmp(cs, ct, tcount);
 }
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 25d9b5adcd42..36b49bd09264 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -77,5 +77,5 @@ static inline struct ovl_inode *OVL_I(struct inode *inode)
 
 static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
 {
-	return lockless_dereference(oi->__upperdentry);
+	return READ_ONCE(oi->__upperdentry);
 }
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 0f85ee9c3268..c67a7703296b 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -754,7 +754,7 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
 	if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
 		struct inode *inode = file_inode(file);
 
-		realfile = lockless_dereference(od->upperfile);
+		realfile = READ_ONCE(od->upperfile);
 		if (!realfile) {
 			struct path upperpath;
 
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c714239f453f..4517662f128c 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -242,6 +242,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 		__read_once_size(&(x), __u.__c, sizeof(x));		\
 	else								\
 		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
+	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
 	__u.__val;							\
 })
 #define READ_ONCE(x) __READ_ONCE(x, 1)
@@ -345,24 +346,4 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 	(volatile typeof(x) *)&(x); })
 #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
 
-/**
- * lockless_dereference() - safely load a pointer for later dereference
- * @p: The pointer to load
- *
- * Similar to rcu_dereference(), but for situations where the pointed-to
- * object's lifetime is managed by something other than RCU.  That
- * "something other" might be reference counting or simple immortality.
- *
- * The seemingly unused variable ___typecheck_p validates that @p is
- * indeed a pointer type by using a pointer to typeof(*p) as the type.
- * Taking a pointer to typeof(*p) again is needed in case p is void *.
- */
-#define lockless_dereference(p) \
-({ \
-	typeof(p) _________p1 = READ_ONCE(p); \
-	typeof(*(p)) *___typecheck_p __maybe_unused; \
-	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
-	(_________p1); \
-})
-
 #endif /* __LINUX_COMPILER_H */
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index b1fd8bf85fdc..3a2bb7d8ed4d 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -274,7 +274,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
  */
 #define list_entry_rcu(ptr, type, member) \
-	container_of(lockless_dereference(ptr), type, member)
+	container_of(READ_ONCE(ptr), type, member)
 
 /**
  * Where are list_empty_rcu() and list_first_entry_rcu()?
@@ -367,7 +367,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * example is when items are added to the list, but never deleted.
  */
 #define list_entry_lockless(ptr, type, member) \
-	container_of((typeof(ptr))lockless_dereference(ptr), type, member)
+	container_of((typeof(ptr))READ_ONCE(ptr), type, member)
 
 /**
  * list_for_each_entry_lockless - iterate over rcu list of given type
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index de50d8a4cf41..380a3aeb09d7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -346,7 +346,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 #define __rcu_dereference_check(p, c, space) \
 ({ \
 	/* Dependency order vs. p above. */ \
-	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
+	typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
 	rcu_dereference_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(________p1)); \
@@ -360,7 +360,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 #define rcu_dereference_raw(p) \
 ({ \
 	/* Dependency order vs. p above. */ \
-	typeof(p) ________p1 = lockless_dereference(p); \
+	typeof(p) ________p1 = READ_ONCE(p); \
 	((typeof(*p) __force __kernel *)(________p1)); \
 })
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6bc21e202ae4..417812ce0099 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4231,7 +4231,7 @@ static void perf_remove_from_owner(struct perf_event *event)
 	 * indeed free this event, otherwise we need to serialize on
 	 * owner->perf_event_mutex.
 	 */
-	owner = lockless_dereference(event->owner);
+	owner = READ_ONCE(event->owner);
 	if (owner) {
 		/*
 		 * Since delayed_put_task_struct() also drops the last
@@ -4328,7 +4328,7 @@ int perf_event_release_kernel(struct perf_event *event)
 		 * Cannot change, child events are not migrated, see the
 		 * comment with perf_event_ctx_lock_nested().
 		 */
-		ctx = lockless_dereference(child->ctx);
+		ctx = READ_ONCE(child->ctx);
 		/*
 		 * Since child_mutex nests inside ctx::mutex, we must jump
 		 * through hoops. We start by grabbing a reference on the ctx.
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index bb3a38005b9c..1daa8b61a268 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -189,7 +189,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
 	u32 ret = SECCOMP_RET_ALLOW;
 	/* Make sure cross-thread synced filter points somewhere sane. */
 	struct seccomp_filter *f =
-			lockless_dereference(current->seccomp.filter);
+			READ_ONCE(current->seccomp.filter);
 
 	/* Ensure unexpected behavior doesn't result in failing open. */
 	if (unlikely(WARN_ON(f == NULL)))
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 836a72a66fba..9a9f262fc53d 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -67,7 +67,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
 	 * we raced with task_work_run(), *pprev == NULL/exited.
 	 */
 	raw_spin_lock_irqsave(&task->pi_lock, flags);
-	while ((work = lockless_dereference(*pprev))) {
+	while ((work = READ_ONCE(*pprev))) {
 		if (work->func != func)
 			pprev = &work->next;
 		else if (cmpxchg(pprev, work, work->next) == work)
diff --git a/mm/slab.h b/mm/slab.h
index 073362816acc..8894f811a89d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -258,7 +258,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx)
 	 * memcg_caches issues a write barrier to match this (see
 	 * memcg_create_kmem_cache()).
 	 */
-	cachep = lockless_dereference(arr->entries[idx]);
+	cachep = READ_ONCE(arr->entries[idx]);
 	rcu_read_unlock();
 
 	return cachep;
-- 
2.1.4

[PATCH 3/3] alpha: atomics: Add smp_read_barrier_depends() to release/relaxed atomics

[Will Deacon]

As part of the fight against smp_read_barrier_depends(), we require
dependency ordering to be preserved when a dependency is headed by a load
performed using an atomic operation.

This patch adds smp_read_barrier_depends() to the _release and _relaxed
atomics on alpha, which otherwise lack anything to enforce dependency
ordering.

Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 arch/alpha/include/asm/atomic.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/alpha/include/asm/atomic.h b/arch/alpha/include/asm/atomic.h
index 498933a7df97..16961a3f45ba 100644
--- a/arch/alpha/include/asm/atomic.h
+++ b/arch/alpha/include/asm/atomic.h
@@ -13,6 +13,15 @@
  * than regular operations.
  */
 
+/*
+ * To ensure dependency ordering is preserved for the _relaxed and
+ * _release atomics, an smp_read_barrier_depends() is unconditionally
+ * inserted into the _relaxed variants, which are used to build the
+ * barriered versions. To avoid redundant back-to-back fences, we can
+ * define the _acquire and _fence versions explicitly.
+ */
+#define __atomic_op_acquire(op, args...)	op##_relaxed(args)
+#define __atomic_op_fence			__atomic_op_release
 
 #define ATOMIC_INIT(i)		{ (i) }
 #define ATOMIC64_INIT(i)	{ (i) }
@@ -60,6 +69,7 @@ static inline int atomic_##op##_return_relaxed(int i, atomic_t *v)	\
 	".previous"							\
 	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
 	:"Ir" (i), "m" (v->counter) : "memory");			\
+	smp_read_barrier_depends();					\
 	return result;							\
 }
 
@@ -77,6 +87,7 @@ static inline int atomic_fetch_##op##_relaxed(int i, atomic_t *v)	\
 	".previous"							\
 	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
 	:"Ir" (i), "m" (v->counter) : "memory");			\
+	smp_read_barrier_depends();					\
 	return result;							\
 }
 
@@ -111,6 +122,7 @@ static __inline__ long atomic64_##op##_return_relaxed(long i, atomic64_t * v)	\
 	".previous"							\
 	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
 	:"Ir" (i), "m" (v->counter) : "memory");			\
+	smp_read_barrier_depends();					\
 	return result;							\
 }
 
@@ -128,6 +140,7 @@ static __inline__ long atomic64_fetch_##op##_relaxed(long i, atomic64_t * v)	\
 	".previous"							\
 	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
 	:"Ir" (i), "m" (v->counter) : "memory");			\
+	smp_read_barrier_depends();					\
 	return result;							\
 }
 
-- 
2.1.4

Re: [PATCH 2/3] locking/barriers: Kill lockless_dereference

[Paul E. McKenney]

On Thu, Oct 12, 2017 at 03:26:16PM +0100, Will Deacon wrote:
> lockless_dereference is a nice idea, but its gained little traction in
> kernel code since it's introduction three years ago. This is partly
> because it's a pain to type, but also because using READ_ONCE instead
> will work correctly on all architectures apart from Alpha, which is a
> fully supported but somewhat niche architecture these days.
> 
> This patch moves smp_read_barrier_depends() (a NOP on all architectures
> other than Alpha) from lockless_dereference into READ_ONCE, converts
> the few actual users over to READ_ONCE and then finally removes
> lockless_dereference altogether.
> 
> Signed-off-by: Will Deacon <will.deacon@arm.com>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  Documentation/memory-barriers.txt                   | 12 ------------
>  .../translations/ko_KR/memory-barriers.txt          | 12 ------------
>  arch/x86/events/core.c                              |  2 +-
>  arch/x86/include/asm/mmu_context.h                  |  4 ++--
>  arch/x86/kernel/ldt.c                               |  2 +-
>  drivers/md/dm-mpath.c                               | 20 ++++++++++----------
>  fs/dcache.c                                         |  4 ++--
>  fs/overlayfs/ovl_entry.h                            |  2 +-
>  fs/overlayfs/readdir.c                              |  2 +-
>  include/linux/compiler.h                            | 21 +--------------------
>  include/linux/rculist.h                             |  4 ++--
>  include/linux/rcupdate.h                            |  4 ++--
>  kernel/events/core.c                                |  4 ++--
>  kernel/seccomp.c                                    |  2 +-
>  kernel/task_work.c                                  |  2 +-
>  mm/slab.h                                           |  2 +-
>  16 files changed, 28 insertions(+), 71 deletions(-)
> 
> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> index b759a60624fd..470a682f3fa4 100644
> --- a/Documentation/memory-barriers.txt
> +++ b/Documentation/memory-barriers.txt
> @@ -1886,18 +1886,6 @@ There are some more advanced barrier functions:
>       See Documentation/atomic_{t,bitops}.txt for more information.
> 
> 
> - (*) lockless_dereference();
> -
> -     This can be thought of as a pointer-fetch wrapper around the
> -     smp_read_barrier_depends() data-dependency barrier.
> -
> -     This is also similar to rcu_dereference(), but in cases where
> -     object lifetime is handled by some mechanism other than RCU, for
> -     example, when the objects removed only when the system goes down.
> -     In addition, lockless_dereference() is used in some data structures
> -     that can be used both with and without RCU.
> -
> -
>   (*) dma_wmb();
>   (*) dma_rmb();
> 
> diff --git a/Documentation/translations/ko_KR/memory-barriers.txt b/Documentation/translations/ko_KR/memory-barriers.txt
> index a7a813258013..ec3b46e27b7a 100644
> --- a/Documentation/translations/ko_KR/memory-barriers.txt
> +++ b/Documentation/translations/ko_KR/memory-barriers.txt
> @@ -1858,18 +1858,6 @@ Mandatory 배리어들은 SMP 시스템에서도 UP 시스템에서도 SMP 효
>       참고하세요.
> 
> 
> - (*) lockless_dereference();
> -
> -     이 함수는 smp_read_barrier_depends() 데이터 의존성 배리어를 사용하는
> -     포인터 읽어오기 래퍼(wrapper) 함수로 생각될 수 있습니다.
> -
> -     객체의 라이프타임이 RCU 외의 메커니즘으로 관리된다는 점을 제외하면
> -     rcu_dereference() 와도 유사한데, 예를 들면 객체가 시스템이 꺼질 때에만
> -     제거되는 경우 등입니다.  또한, lockless_dereference() 은 RCU 와 함께
> -     사용될수도, RCU 없이 사용될 수도 있는 일부 데이터 구조에 사용되고
> -     있습니다.
> -
> -
>   (*) dma_wmb();
>   (*) dma_rmb();
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 80534d3c2480..589af1eec7c1 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -2371,7 +2371,7 @@ static unsigned long get_segment_base(unsigned int segment)
>  		struct ldt_struct *ldt;
> 
>  		/* IRQs are off, so this synchronizes with smp_store_release */
> -		ldt = lockless_dereference(current->active_mm->context.ldt);
> +		ldt = READ_ONCE(current->active_mm->context.ldt);
>  		if (!ldt || idx >= ldt->nr_entries)
>  			return 0;
> 
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index c120b5db178a..9037a4e546e8 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -72,8 +72,8 @@ static inline void load_mm_ldt(struct mm_struct *mm)
>  #ifdef CONFIG_MODIFY_LDT_SYSCALL
>  	struct ldt_struct *ldt;
> 
> -	/* lockless_dereference synchronizes with smp_store_release */
> -	ldt = lockless_dereference(mm->context.ldt);
> +	/* READ_ONCE synchronizes with smp_store_release */
> +	ldt = READ_ONCE(mm->context.ldt);
> 
>  	/*
>  	 * Any change to mm->context.ldt is followed by an IPI to all
> diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
> index f0e64db18ac8..0a21390642c4 100644
> --- a/arch/x86/kernel/ldt.c
> +++ b/arch/x86/kernel/ldt.c
> @@ -101,7 +101,7 @@ static void finalize_ldt_struct(struct ldt_struct *ldt)
>  static void install_ldt(struct mm_struct *current_mm,
>  			struct ldt_struct *ldt)
>  {
> -	/* Synchronizes with lockless_dereference in load_mm_ldt. */
> +	/* Synchronizes with READ_ONCE in load_mm_ldt. */
>  	smp_store_release(&current_mm->context.ldt, ldt);
> 
>  	/* Activate the LDT for all CPUs using current_mm. */
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 11f273d2f018..3f88c9d32f7e 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -366,7 +366,7 @@ static struct pgpath *choose_path_in_pg(struct multipath *m,
> 
>  	pgpath = path_to_pgpath(path);
> 
> -	if (unlikely(lockless_dereference(m->current_pg) != pg)) {
> +	if (unlikely(READ_ONCE(m->current_pg) != pg)) {
>  		/* Only update current_pgpath if pg changed */
>  		spin_lock_irqsave(&m->lock, flags);
>  		m->current_pgpath = pgpath;
> @@ -390,7 +390,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
>  	}
> 
>  	/* Were we instructed to switch PG? */
> -	if (lockless_dereference(m->next_pg)) {
> +	if (READ_ONCE(m->next_pg)) {
>  		spin_lock_irqsave(&m->lock, flags);
>  		pg = m->next_pg;
>  		if (!pg) {
> @@ -406,7 +406,7 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
> 
>  	/* Don't change PG until it has no remaining paths */
>  check_current_pg:
> -	pg = lockless_dereference(m->current_pg);
> +	pg = READ_ONCE(m->current_pg);
>  	if (pg) {
>  		pgpath = choose_path_in_pg(m, pg, nr_bytes);
>  		if (!IS_ERR_OR_NULL(pgpath))
> @@ -473,7 +473,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
>  	struct request *clone;
> 
>  	/* Do we need to select a new pgpath? */
> -	pgpath = lockless_dereference(m->current_pgpath);
> +	pgpath = READ_ONCE(m->current_pgpath);
>  	if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))
>  		pgpath = choose_pgpath(m, nr_bytes);
> 
> @@ -535,7 +535,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
>  	bool queue_io;
> 
>  	/* Do we need to select a new pgpath? */
> -	pgpath = lockless_dereference(m->current_pgpath);
> +	pgpath = READ_ONCE(m->current_pgpath);
>  	queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
>  	if (!pgpath || !queue_io)
>  		pgpath = choose_pgpath(m, nr_bytes);
> @@ -1804,7 +1804,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
>  	struct pgpath *current_pgpath;
>  	int r;
> 
> -	current_pgpath = lockless_dereference(m->current_pgpath);
> +	current_pgpath = READ_ONCE(m->current_pgpath);
>  	if (!current_pgpath)
>  		current_pgpath = choose_pgpath(m, 0);
> 
> @@ -1826,7 +1826,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
>  	}
> 
>  	if (r == -ENOTCONN) {
> -		if (!lockless_dereference(m->current_pg)) {
> +		if (!READ_ONCE(m->current_pg)) {
>  			/* Path status changed, redo selection */
>  			(void) choose_pgpath(m, 0);
>  		}
> @@ -1895,9 +1895,9 @@ static int multipath_busy(struct dm_target *ti)
>  		return (m->queue_mode != DM_TYPE_MQ_REQUEST_BASED);
> 
>  	/* Guess which priority_group will be used at next mapping time */
> -	pg = lockless_dereference(m->current_pg);
> -	next_pg = lockless_dereference(m->next_pg);
> -	if (unlikely(!lockless_dereference(m->current_pgpath) && next_pg))
> +	pg = READ_ONCE(m->current_pg);
> +	next_pg = READ_ONCE(m->next_pg);
> +	if (unlikely(!READ_ONCE(m->current_pgpath) && next_pg))
>  		pg = next_pg;
> 
>  	if (!pg) {
> diff --git a/fs/dcache.c b/fs/dcache.c
> index f90141387f01..34c852af215c 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -231,7 +231,7 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
>  {
>  	/*
>  	 * Be careful about RCU walk racing with rename:
> -	 * use 'lockless_dereference' to fetch the name pointer.
> +	 * use 'READ_ONCE' to fetch the name pointer.
>  	 *
>  	 * NOTE! Even if a rename will mean that the length
>  	 * was not loaded atomically, we don't care. The
> @@ -245,7 +245,7 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
>  	 * early because the data cannot match (there can
>  	 * be no NUL in the ct/tcount data)
>  	 */
> -	const unsigned char *cs = lockless_dereference(dentry->d_name.name);
> +	const unsigned char *cs = READ_ONCE(dentry->d_name.name);
> 
>  	return dentry_string_cmp(cs, ct, tcount);
>  }
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 25d9b5adcd42..36b49bd09264 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -77,5 +77,5 @@ static inline struct ovl_inode *OVL_I(struct inode *inode)
> 
>  static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
>  {
> -	return lockless_dereference(oi->__upperdentry);
> +	return READ_ONCE(oi->__upperdentry);
>  }
> diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
> index 0f85ee9c3268..c67a7703296b 100644
> --- a/fs/overlayfs/readdir.c
> +++ b/fs/overlayfs/readdir.c
> @@ -754,7 +754,7 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
>  	if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
>  		struct inode *inode = file_inode(file);
> 
> -		realfile = lockless_dereference(od->upperfile);
> +		realfile = READ_ONCE(od->upperfile);
>  		if (!realfile) {
>  			struct path upperpath;
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index c714239f453f..4517662f128c 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -242,6 +242,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>  		__read_once_size(&(x), __u.__c, sizeof(x));		\
>  	else								\
>  		__read_once_size_nocheck(&(x), __u.__c, sizeof(x));	\
> +	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
>  	__u.__val;							\
>  })
>  #define READ_ONCE(x) __READ_ONCE(x, 1)
> @@ -345,24 +346,4 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>  	(volatile typeof(x) *)&(x); })
>  #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
> 
> -/**
> - * lockless_dereference() - safely load a pointer for later dereference
> - * @p: The pointer to load
> - *
> - * Similar to rcu_dereference(), but for situations where the pointed-to
> - * object's lifetime is managed by something other than RCU.  That
> - * "something other" might be reference counting or simple immortality.
> - *
> - * The seemingly unused variable ___typecheck_p validates that @p is
> - * indeed a pointer type by using a pointer to typeof(*p) as the type.
> - * Taking a pointer to typeof(*p) again is needed in case p is void *.
> - */
> -#define lockless_dereference(p) \
> -({ \
> -	typeof(p) _________p1 = READ_ONCE(p); \
> -	typeof(*(p)) *___typecheck_p __maybe_unused; \
> -	smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
> -	(_________p1); \
> -})
> -
>  #endif /* __LINUX_COMPILER_H */
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index b1fd8bf85fdc..3a2bb7d8ed4d 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -274,7 +274,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
>   * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
>   */
>  #define list_entry_rcu(ptr, type, member) \
> -	container_of(lockless_dereference(ptr), type, member)
> +	container_of(READ_ONCE(ptr), type, member)
> 
>  /**
>   * Where are list_empty_rcu() and list_first_entry_rcu()?
> @@ -367,7 +367,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
>   * example is when items are added to the list, but never deleted.
>   */
>  #define list_entry_lockless(ptr, type, member) \
> -	container_of((typeof(ptr))lockless_dereference(ptr), type, member)
> +	container_of((typeof(ptr))READ_ONCE(ptr), type, member)
> 
>  /**
>   * list_for_each_entry_lockless - iterate over rcu list of given type
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index de50d8a4cf41..380a3aeb09d7 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -346,7 +346,7 @@ static inline void rcu_preempt_sleep_check(void) { }
>  #define __rcu_dereference_check(p, c, space) \
>  ({ \
>  	/* Dependency order vs. p above. */ \
> -	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
> +	typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
>  	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
>  	rcu_dereference_sparse(p, space); \
>  	((typeof(*p) __force __kernel *)(________p1)); \
> @@ -360,7 +360,7 @@ static inline void rcu_preempt_sleep_check(void) { }
>  #define rcu_dereference_raw(p) \
>  ({ \
>  	/* Dependency order vs. p above. */ \
> -	typeof(p) ________p1 = lockless_dereference(p); \
> +	typeof(p) ________p1 = READ_ONCE(p); \
>  	((typeof(*p) __force __kernel *)(________p1)); \
>  })
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 6bc21e202ae4..417812ce0099 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4231,7 +4231,7 @@ static void perf_remove_from_owner(struct perf_event *event)
>  	 * indeed free this event, otherwise we need to serialize on
>  	 * owner->perf_event_mutex.
>  	 */
> -	owner = lockless_dereference(event->owner);
> +	owner = READ_ONCE(event->owner);
>  	if (owner) {
>  		/*
>  		 * Since delayed_put_task_struct() also drops the last
> @@ -4328,7 +4328,7 @@ int perf_event_release_kernel(struct perf_event *event)
>  		 * Cannot change, child events are not migrated, see the
>  		 * comment with perf_event_ctx_lock_nested().
>  		 */
> -		ctx = lockless_dereference(child->ctx);
> +		ctx = READ_ONCE(child->ctx);
>  		/*
>  		 * Since child_mutex nests inside ctx::mutex, we must jump
>  		 * through hoops. We start by grabbing a reference on the ctx.
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index bb3a38005b9c..1daa8b61a268 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -189,7 +189,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
>  	u32 ret = SECCOMP_RET_ALLOW;
>  	/* Make sure cross-thread synced filter points somewhere sane. */
>  	struct seccomp_filter *f =
> -			lockless_dereference(current->seccomp.filter);
> +			READ_ONCE(current->seccomp.filter);
> 
>  	/* Ensure unexpected behavior doesn't result in failing open. */
>  	if (unlikely(WARN_ON(f == NULL)))
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 836a72a66fba..9a9f262fc53d 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -67,7 +67,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
>  	 * we raced with task_work_run(), *pprev == NULL/exited.
>  	 */
>  	raw_spin_lock_irqsave(&task->pi_lock, flags);
> -	while ((work = lockless_dereference(*pprev))) {
> +	while ((work = READ_ONCE(*pprev))) {
>  		if (work->func != func)
>  			pprev = &work->next;
>  		else if (cmpxchg(pprev, work, work->next) == work)
> diff --git a/mm/slab.h b/mm/slab.h
> index 073362816acc..8894f811a89d 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -258,7 +258,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx)
>  	 * memcg_caches issues a write barrier to match this (see
>  	 * memcg_create_kmem_cache()).
>  	 */
> -	cachep = lockless_dereference(arr->entries[idx]);
> +	cachep = READ_ONCE(arr->entries[idx]);
>  	rcu_read_unlock();
> 
>  	return cachep;
> -- 
> 2.1.4
> 

Re: [PATCH 3/3] alpha: atomics: Add smp_read_barrier_depends() to release/relaxed atomics

[Paul E. McKenney]

On Thu, Oct 12, 2017 at 03:26:17PM +0100, Will Deacon wrote:
> As part of the fight against smp_read_barrier_depends(), we require
> dependency ordering to be preserved when a dependency is headed by a load
> performed using an atomic operation.
> 
> This patch adds smp_read_barrier_depends() to the _release and _relaxed
> atomics on alpha, which otherwise lack anything to enforce dependency
> ordering.
> 
> Signed-off-by: Will Deacon <will.deacon@arm.com>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
>  arch/alpha/include/asm/atomic.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/alpha/include/asm/atomic.h b/arch/alpha/include/asm/atomic.h
> index 498933a7df97..16961a3f45ba 100644
> --- a/arch/alpha/include/asm/atomic.h
> +++ b/arch/alpha/include/asm/atomic.h
> @@ -13,6 +13,15 @@
>   * than regular operations.
>   */
> 
> +/*
> + * To ensure dependency ordering is preserved for the _relaxed and
> + * _release atomics, an smp_read_barrier_depends() is unconditionally
> + * inserted into the _relaxed variants, which are used to build the
> + * barriered versions. To avoid redundant back-to-back fences, we can
> + * define the _acquire and _fence versions explicitly.
> + */
> +#define __atomic_op_acquire(op, args...)	op##_relaxed(args)
> +#define __atomic_op_fence			__atomic_op_release
> 
>  #define ATOMIC_INIT(i)		{ (i) }
>  #define ATOMIC64_INIT(i)	{ (i) }
> @@ -60,6 +69,7 @@ static inline int atomic_##op##_return_relaxed(int i, atomic_t *v)	\
>  	".previous"							\
>  	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
>  	:"Ir" (i), "m" (v->counter) : "memory");			\
> +	smp_read_barrier_depends();					\
>  	return result;							\
>  }
> 
> @@ -77,6 +87,7 @@ static inline int atomic_fetch_##op##_relaxed(int i, atomic_t *v)	\
>  	".previous"							\
>  	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
>  	:"Ir" (i), "m" (v->counter) : "memory");			\
> +	smp_read_barrier_depends();					\
>  	return result;							\
>  }
> 
> @@ -111,6 +122,7 @@ static __inline__ long atomic64_##op##_return_relaxed(long i, atomic64_t * v)	\
>  	".previous"							\
>  	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
>  	:"Ir" (i), "m" (v->counter) : "memory");			\
> +	smp_read_barrier_depends();					\
>  	return result;							\
>  }
> 
> @@ -128,6 +140,7 @@ static __inline__ long atomic64_fetch_##op##_relaxed(long i, atomic64_t * v)	\
>  	".previous"							\
>  	:"=&r" (temp), "=m" (v->counter), "=&r" (result)		\
>  	:"Ir" (i), "m" (v->counter) : "memory");			\
> +	smp_read_barrier_depends();					\
>  	return result;							\
>  }
> 
> -- 
> 2.1.4
>