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new list.h with {READ,WRITE}_ONCE

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This commit is contained in:
Bruno Raoult
2022-03-18 17:25:39 +01:00
parent d4ec54ed5b
commit 1f835c10c5
2 changed files with 147 additions and 22 deletions
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45
2021/include/list.h
View File

@@ -10,6 +10,7 @@
#include <stddef.h>
#include <stdbool.h>
#include "rwonce.h"
/************ originally in <include/linux/types.h> */
struct list_head {
@@ -61,7 +62,7 @@ struct hlist_node {
*/
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
WRITE_ONCE(list->next, list);
list->prev = list;
}
@@ -78,7 +79,7 @@ static inline void __list_add(struct list_head *new,
next->prev = new;
new->next = next;
new->prev = prev;
prev->next = new;
WRITE_ONCE(prev->next, new);
}
/**
@@ -118,7 +119,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
next->prev = prev;
prev->next = next;
WRITE_ONCE(prev->next, next);
}
/*
@@ -284,7 +285,7 @@ static inline int list_is_last(const struct list_head *list,
*/
static inline int list_empty(const struct list_head *head)
{
return head->next == head;
return READ_ONCE(head->next) == head;
}
/**
@@ -510,7 +511,7 @@ static inline void list_splice_tail_init(struct list_head *list,
*/
#define list_first_entry_or_null(ptr, type, member) ({ \
struct list_head *head__ = (ptr); \
struct list_head *pos__ = head__->next; \
struct list_head *pos__ = READ_ONCE(head__->next); \
pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
})
@@ -786,7 +787,7 @@ static inline int hlist_unhashed(const struct hlist_node *h)
*/
static inline int hlist_unhashed_lockless(const struct hlist_node *h)
{
return !h->pprev;
return !READ_ONCE(h->pprev);
}
/**
@@ -795,7 +796,7 @@ static inline int hlist_unhashed_lockless(const struct hlist_node *h)
*/
static inline int hlist_empty(const struct hlist_head *h)
{
return !h->first;
return !READ_ONCE(h->first);
}
static inline void __hlist_del(struct hlist_node *n)
@@ -803,9 +804,9 @@ static inline void __hlist_del(struct hlist_node *n)
struct hlist_node *next = n->next;
struct hlist_node **pprev = n->pprev;
*pprev = next;
WRITE_ONCE(*pprev, next);
if (next)
next->pprev = pprev;
WRITE_ONCE(next->pprev, pprev);
}
/**
@@ -847,11 +848,11 @@ static inline void hlist_del_init(struct hlist_node *n)
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
struct hlist_node *first = h->first;
n->next = first;
WRITE_ONCE(n->next, first);
if (first)
first->pprev = &n->next;
h->first = n;
n->pprev = &h->first;
WRITE_ONCE(first->pprev, &n->next);
WRITE_ONCE(h->first, n);
WRITE_ONCE(n->pprev, &h->first);
}
/**
@@ -862,10 +863,10 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
static inline void hlist_add_before(struct hlist_node *n,
struct hlist_node *next)
{
n->pprev = next->pprev;
n->next = next;
next->pprev = &n->next;
*(n->pprev) = n;
WRITE_ONCE(n->pprev, next->pprev);
WRITE_ONCE(n->next, next);
WRITE_ONCE(next->pprev, &n->next);
WRITE_ONCE(*(n->pprev), n);
}
/**
@@ -876,12 +877,12 @@ static inline void hlist_add_before(struct hlist_node *n,
static inline void hlist_add_behind(struct hlist_node *n,
struct hlist_node *prev)
{
n->next = prev->next;
prev->next = n;
n->pprev = &prev->next;
WRITE_ONCE(n->next, prev->next);
WRITE_ONCE(prev->next, n);
WRITE_ONCE(n->pprev, &prev->next);
if (n->next)
n->next->pprev = &n->next;
WRITE_ONCE(n->next->pprev, &n->next);
}
/**
@@ -993,4 +994,4 @@ static inline void hlist_move_list(struct hlist_head *old,
pos && ({ n = pos->member.next; 1; }); \
pos = hlist_entry_safe(n, __typeof__(*pos), member))
#endif
#endif /* __BR_LIST_H */

124
2021/include/rwonce.h Normal file
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@@ -0,0 +1,124 @@
/* SPDX-License-Identifier: GPL-2.0 */
/* adaptation of kernel's <asm-generic/rwonce.h>
* See https://www.kernel.org/doc/Documentation/memory-barriers.txt
*/
/*
* 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 __BR_RWONCE_H
#define __BR_RWONCE_H
/************ originally in <include/linux/compiler_types.h> */
# define __compiletime_error(message) __attribute__((error(message)))
/************ originally in <include/linux/compiler_types.h> */
/*
* __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving
* non-scalar types unchanged.
*/
/*
* Prefer C11 _Generic for better compile-times and simpler code. Note: 'char'
* is not type-compatible with 'signed char', and we define a separate case.
*/
#define __scalar_type_to_expr_cases(type) \
unsigned type: (unsigned type)0, \
signed type: (signed type)0
#define __unqual_scalar_typeof(x) typeof( \
_Generic((x), \
char: (char)0, \
__scalar_type_to_expr_cases(char), \
__scalar_type_to_expr_cases(short), \
__scalar_type_to_expr_cases(int), \
__scalar_type_to_expr_cases(long), \
__scalar_type_to_expr_cases(long long), \
default: (x)))
/* Is this type a native word size -- useful for atomic operations */
#define __native_word(t) \
(sizeof(t) == sizeof(char) || sizeof(t) == sizeof(short) || \
sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
#ifdef __OPTIMIZE__
# define __compiletime_assert(condition, msg, prefix, suffix) \
do { \
extern void prefix ## suffix(void) __compiletime_error(msg); \
if (!(condition)) \
prefix ## suffix(); \
} while (0)
#else
# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
#endif
#define _compiletime_assert(condition, msg, prefix, suffix) \
__compiletime_assert(condition, msg, prefix, suffix)
/**
* compiletime_assert - break build and emit msg if condition is false
* @condition: a compile-time constant condition to check
* @msg: a message to emit if condition is false
*
* In tradition of POSIX assert, this macro will break the build if the
* supplied condition is *false*, emitting the supplied error message if the
* compiler has support to do so.
*/
#define compiletime_assert(condition, msg) \
_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
#define compiletime_assert_atomic_type(t) \
compiletime_assert(__native_word(t), \
"Need native word sized stores/loads for atomicity.")
/************ originally in <asm-generic/rwonce.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)
#endif /* __BR_RWONCE_H */