Re: [PATCH v3 02/19] compiler.h: Split {READ, WRITE}_ONCE definitions out into rwonce.h
On Mon, Jul 13, 2020 at 08:23:22PM +0800, boqun.f...@gmail.com wrote:
> On Fri, Jul 10, 2020 at 05:51:46PM +0100, Will Deacon wrote:
> > diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
> > new file mode 100644
> > index ..92cc2f223cb3
> > --- /dev/null
> > +++ b/include/asm-generic/rwonce.h
> > @@ -0,0 +1,91 @@
> > +/* 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
> > +#include
> > +#include
> > +
> > +#include
> > +
> > +/*
> > + * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
> > + * atomicity or dependency ordering guarantees. Note that this may result
> > + * in tears!
> > + */
> > +#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x)
> > *)&(x))
> > +
> > +#define __READ_ONCE_SCALAR(x)
> > \
> > +({ \
> > + __unqual_scalar_typeof(x) __x = __READ_ONCE(x); \
> > + smp_read_barrier_depends(); \
> > + (typeof(x))__x; \
> > +})
> > +
> > +#define READ_ONCE(x)
> > \
> > +({ \
> > + compiletime_assert_rwonce_type(x); \
>
> Does it make sense if we also move the definition of this compile time
> assertion into rwonce.h too?
Yes, that looks straightforward enough. Thanks for the suggestion!
I'll also try to get this lot into -next this week.
Will
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Re: [PATCH v3 02/19] compiler.h: Split {READ, WRITE}_ONCE definitions out into rwonce.h
On Fri, Jul 10, 2020 at 05:51:46PM +0100, Will Deacon wrote:
> In preparation for allowing architectures to define their own
> implementation of the READ_ONCE() macro, move the generic
> {READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h'
> file and into a new 'rwonce.h' header under 'asm-generic'.
>
> Acked-by: Paul E. McKenney
> Signed-off-by: Will Deacon
> ---
> include/asm-generic/Kbuild| 1 +
> include/asm-generic/barrier.h | 2 +-
> include/asm-generic/rwonce.h | 91 +++
> include/linux/compiler.h | 83 +---
> 4 files changed, 95 insertions(+), 82 deletions(-)
> create mode 100644 include/asm-generic/rwonce.h
>
> 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..8116744bb82c 100644
> --- a/include/asm-generic/barrier.h
> +++ b/include/asm-generic/barrier.h
> @@ -13,7 +13,7 @@
>
> #ifndef __ASSEMBLY__
>
> -#include
> +#include
>
> #ifndef nop
> #define nop()asm volatile ("nop")
> diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
> new file mode 100644
> index ..92cc2f223cb3
> --- /dev/null
> +++ b/include/asm-generic/rwonce.h
> @@ -0,0 +1,91 @@
> +/* 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
> +#include
> +#include
> +
> +#include
> +
> +/*
> + * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
> + * atomicity or dependency ordering guarantees. Note that this may result
> + * in tears!
> + */
> +#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x)
> *)&(x))
> +
> +#define __READ_ONCE_SCALAR(x)
> \
> +({ \
> + __unqual_scalar_typeof(x) __x = __READ_ONCE(x); \
> + smp_read_barrier_depends(); \
> + (typeof(x))__x; \
> +})
> +
> +#define READ_ONCE(x) \
> +({ \
> + compiletime_assert_rwonce_type(x); \
Does it make sense if we also move the definition of this compile time
assertion into rwonce.h too?
Regards,
Boqun
> + __READ_ONCE_SCALAR(x); \
> +})
> +
[...]
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[PATCH v3 02/19] compiler.h: Split {READ, WRITE}_ONCE definitions out into rwonce.h
In preparation for allowing architectures to define their own
implementation of the READ_ONCE() macro, move the generic
{READ,WRITE}_ONCE() definitions out of the unwieldy 'linux/compiler.h'
file and into a new 'rwonce.h' header under 'asm-generic'.
Acked-by: Paul E. McKenney
Signed-off-by: Will Deacon
---
include/asm-generic/Kbuild| 1 +
include/asm-generic/barrier.h | 2 +-
include/asm-generic/rwonce.h | 91 +++
include/linux/compiler.h | 83 +---
4 files changed, 95 insertions(+), 82 deletions(-)
create mode 100644 include/asm-generic/rwonce.h
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..8116744bb82c 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -13,7 +13,7 @@
#ifndef __ASSEMBLY__
-#include
+#include
#ifndef nop
#define nop() asm volatile ("nop")
diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h
new file mode 100644
index ..92cc2f223cb3
--- /dev/null
+++ b/include/asm-generic/rwonce.h
@@ -0,0 +1,91 @@
+/* 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
+#include
+#include
+
+#include
+
+/*
+ * Use __READ_ONCE() instead of READ_ONCE() if you do not require any
+ * atomicity or dependency ordering guarantees. Note that this may result
+ * in tears!
+ */
+#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
+
+#define __READ_ONCE_SCALAR(x) \
+({ \
+ __unqual_scalar_typeof(x) __x = __READ_ONCE(x); \
+ smp_read_barrier_depends(); \
+ (typeof(x))__x; \
+})
+
+#define READ_ONCE(x) \
+({ \
+ compiletime_assert_rwonce_type(x); \
+ __READ_ONCE_SCALAR(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) \
+({ \
+ unsigned long __x; \
+ compiletime_assert(sizeof(x) == sizeof(__x),\
+ "Unsupported access size for READ_ONCE_NOCHECK().");\
+ __x = __read_once_word_nocheck(&(x)); \
+ smp_read_barrier_depends(); \
+ (typeof(x))__x;
