Merge branch 'for-next/read-barrier-depends' into for-next/core

* for-next/read-barrier-depends:
  : Allow architectures to override __READ_ONCE()
  arm64: Reduce the number of header files pulled into vmlinux.lds.S
  compiler.h: Move compiletime_assert() macros into compiler_types.h
  checkpatch: Remove checks relating to [smp_]read_barrier_depends()
  include/linux: Remove smp_read_barrier_depends() from comments
  tools/memory-model: Remove smp_read_barrier_depends() from informal doc
  Documentation/barriers/kokr: Remove references to [smp_]read_barrier_depends()
  Documentation/barriers: Remove references to [smp_]read_barrier_depends()
  locking/barriers: Remove definitions for [smp_]read_barrier_depends()
  alpha: Replace smp_read_barrier_depends() usage with smp_[r]mb()
  vhost: Remove redundant use of read_barrier_depends() barrier
  asm/rwonce: Don't pull <asm/barrier.h> into 'asm-generic/rwonce.h'
  asm/rwonce: Remove smp_read_barrier_depends() invocation
  alpha: Override READ_ONCE() with barriered implementation
  asm/rwonce: Allow __READ_ONCE to be overridden by the architecture
  compiler.h: Split {READ,WRITE}_ONCE definitions out into rwonce.h
  tools: bpf: Use local copy of headers including uapi/linux/filter.h

3 files changed, 92 insertions, 18 deletions

diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 44ec80e70518..74b0612601dd 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -45,6 +45,7 @@ mandatory-y += pci.h
 mandatory-y += percpu.h
 mandatory-y += pgalloc.h
 mandatory-y += preempt.h
+mandatory-y += rwonce.h
 mandatory-y += sections.h
 mandatory-y += serial.h
 mandatory-y += shmparam.h
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 2eacaf7d62f6..fec97dc34de7 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -13,7 +13,7 @@
 
 #ifndef __ASSEMBLY__
 
-#include <linux/compiler.h>
+#include <asm/rwonce.h>
 
 #ifndef nop
 #define nop()	asm volatile ("nop")
@@ -46,10 +46,6 @@
 #define dma_wmb()	wmb()
 #endif
 
-#ifndef read_barrier_depends
-#define read_barrier_depends()		do { } while (0)
-#endif
-
 #ifndef __smp_mb
 #define __smp_mb()	mb()
 #endif
@@ -62,10 +58,6 @@
 #define __smp_wmb()	wmb()
 #endif
 
-#ifndef __smp_read_barrier_depends
-#define __smp_read_barrier_depends()	read_barrier_depends()
-#endif
-
 #ifdef CONFIG_SMP
 
 #ifndef smp_mb
@@ -80,10 +72,6 @@
 #define smp_wmb()	__smp_wmb()
 #endif
 
-#ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends()	__smp_read_barrier_depends()
-#endif
-
 #else	/* !CONFIG_SMP */
 
 #ifndef smp_mb
@@ -98,10 +86,6 @@
 #define smp_wmb()	barrier()
 #endif
 
-#ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends()	do { } while (0)
-#endif
-
 #endif	/* CONFIG_SMP */
 
 #ifndef __smp_store_mb
@@ -196,7 +180,6 @@ do {									\
 #define virt_mb() __smp_mb()
 #define virt_rmb() __smp_rmb()
 #define virt_wmb() __smp_wmb()
-#define virt_read_barrier_depends() __smp_read_barrier_depends()
 #define virt_store_mb(var, value) __smp_store_mb(var, value)
 #define virt_mb__before_atomic() __smp_mb__before_atomic()
 #define virt_mb__after_atomic()	__smp_mb__after_atomic()
diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
new file mode 100644
index 000000000000..8d0a6280e982
--- /dev/null
+++ b/include/asm-generic/rwonce.h
@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Prevent the compiler from merging or refetching reads or writes. The
+ * compiler is also forbidden from reordering successive instances of
+ * READ_ONCE and WRITE_ONCE, but only when the compiler is aware of some
+ * particular ordering. One way to make the compiler aware of ordering is to
+ * put the two invocations of READ_ONCE or WRITE_ONCE in different C
+ * statements.
+ *
+ * These two macros will also work on aggregate data types like structs or
+ * unions.
+ *
+ * Their two major use cases are: (1) Mediating communication between
+ * process-level code and irq/NMI handlers, all running on the same CPU,
+ * and (2) Ensuring that the compiler does not fold, spindle, or otherwise
+ * mutilate accesses that either do not require ordering or that interact
+ * with an explicit memory barrier or atomic instruction that provides the
+ * required ordering.
+ */
+#ifndef __ASM_GENERIC_RWONCE_H
+#define __ASM_GENERIC_RWONCE_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/compiler_types.h>
+#include <linux/kasan-checks.h>
+#include <linux/kcsan-checks.h>
+
+/*
+ * Yes, this permits 64-bit accesses on 32-bit architectures. These will
+ * actually be atomic in some cases (namely Armv7 + LPAE), but for others we
+ * rely on the access being split into 2x32-bit accesses for a 32-bit quantity
+ * (e.g. a virtual address) and a strong prevailing wind.
+ */
+#define compiletime_assert_rwonce_type(t)					\
+	compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long),	\
+		"Unsupported access size for {READ,WRITE}_ONCE().")
+
+/*
+ * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
+ * atomicity. Note that this may result in tears!
+ */
+#ifndef __READ_ONCE
+#define __READ_ONCE(x)	(*(const volatile __unqual_scalar_typeof(x) *)&(x))
+#endif
+
+#define READ_ONCE(x)							\
+({									\
+	compiletime_assert_rwonce_type(x);				\
+	__READ_ONCE(x);							\
+})
+
+#define __WRITE_ONCE(x, val)						\
+do {									\
+	*(volatile typeof(x) *)&(x) = (val);				\
+} while (0)
+
+#define WRITE_ONCE(x, val)						\
+do {									\
+	compiletime_assert_rwonce_type(x);				\
+	__WRITE_ONCE(x, val);						\
+} while (0)
+
+static __no_sanitize_or_inline
+unsigned long __read_once_word_nocheck(const void *addr)
+{
+	return __READ_ONCE(*(unsigned long *)addr);
+}
+
+/*
+ * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need to load a
+ * word from memory atomically but without telling KASAN/KCSAN. This is
+ * usually used by unwinding code when walking the stack of a running process.
+ */
+#define READ_ONCE_NOCHECK(x)						\
+({									\
+	compiletime_assert(sizeof(x) == sizeof(unsigned long),		\
+		"Unsupported access size for READ_ONCE_NOCHECK().");	\
+	(typeof(x))__read_once_word_nocheck(&(x));			\
+})
+
+static __no_kasan_or_inline
+unsigned long read_word_at_a_time(const void *addr)
+{
+	kasan_check_read(addr, 1);
+	return *(unsigned long *)addr;
+}
+
+#endif /* __ASSEMBLY__ */
+#endif	/* __ASM_GENERIC_RWONCE_H */