Linux社区关于链表的bug讨论我们要看一下

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef LIST_H
#define LIST_H

/*
 * Copied from include/linux/...
 */

#undef offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

/**
 * container_of - cast a member of a structure out to the containing structure
 * @ptr: the pointer to the member.
 * @type: the type of the container struct this is embedded in.
 * @member: the name of the member within the struct.
 *
 */
#define container_of(ptr, type, member) ({ \
  const typeof( ((type *)0)->member ) *__mptr = (ptr); \
  (type *)( (char *)__mptr - offsetof(type,member) );})


struct list_head {
  struct list_head *next, *prev;
};


#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
  struct list_head name = LIST_HEAD_INIT(name)

/**
 * list_entry - get the struct for this entry
 * @ptr: the &struct list_head pointer.
 * @type: the type of the struct this is embedded in.
 * @member: the name of the list_head within the struct.
 */
#define list_entry(ptr, type, member) \
  container_of(ptr, type, member)

/**
 * list_for_each_entry - iterate over list of given type
 * @pos: the type * to use as a loop cursor.
 * @head: the head for your list.
 * @member: the name of the list_head within the struct.
 */
#define list_for_each_entry(pos, head, member) \
  for (pos = list_entry((head)->next, typeof(*pos), member); \
       &pos->member != (head); \
       pos = list_entry(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @pos: the type * to use as a loop cursor.
 * @n: another type * to use as temporary storage
 * @head: the head for your list.
 * @member: the name of the list_head within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member) \
  for (pos = list_entry((head)->next, typeof(*pos), member), \
    n = list_entry(pos->member.next, typeof(*pos), member); \
       &pos->member != (head); \
       pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_empty - tests whether a list is empty
 * @head: the list to test.
 */
static inline int list_empty(const struct list_head *head)
{
  return head->next == head;
}

/*
 * Insert a new entry between two known consecutive entries.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_add(struct list_head *_new,
            struct list_head *prev,
            struct list_head *next)
{
  next->prev = _new;
  _new->next = next;
  _new->prev = prev;
  prev->next = _new;
}

/**
 * list_add_tail - add a new entry
 * @new: new entry to be added
 * @head: list head to add it before
 *
 * Insert a new entry before the specified head.
 * This is useful for implementing queues.
 */
static inline void list_add_tail(struct list_head *_new, struct list_head *head)
{
  __list_add(_new, head->prev, head);
}

/*
 * Delete a list entry by making the prev/next entries
 * point to each other.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
  next->prev = prev;
  prev->next = next;
}

#define LIST_POISON1 ((void *) 0x00100100)
#define LIST_POISON2 ((void *) 0x00200200)
/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty() on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry)
{
  __list_del(entry->prev, entry->next);
  entry->next = (struct list_head*)LIST_POISON1;
  entry->prev = (struct list_head*)LIST_POISON2;
}
#endif

#include 
#include 
#include 
#include "list.h"

struct stu_example {
  struct list_head of_node;
  int age;
};

static LIST_HEAD(stu_list_head);
#define LIST_LEN 10

int main( )
{
  int i = 0;
  /*初始化链表*/
  struct stu_example stu_list[LIST_LEN];
  struct stu_example *tmp = NULL;
  
  for  (i=0; i < LIST_LEN; i++) {
    list_add_tail(&stu_list[i],&stu_list_head);
    stu_list[i].age = i + 20;
  }
  
  /*遍历链表*/ 
  list_for_each_entry(tmp, &stu_list_head, of_node) {
    printf("age=%d\n",tmp->age);
  }
  
  /*删除链表*/
  list_del(&stu_list_head);
  
  printf("Hello,world\n");
  return 0;
}

+/* Override the default implementation from linux/nospec.h. */
+#define select_nospec(cond, exptrue, expfalse) \
+({ \
+ typeof(exptrue) _out = (exptrue); \
+ \
+ asm volatile("test %1, %1\n\t"          \
+ "cmove %2, %0"            \
+ : "+r" (_out) \
+ : "r" (cond), "r" (expfalse)); \
+ _out; \
+})
+
 /* Prevent speculative execution past this barrier. */
 #define barrier_nospec() alternative("", "lfence", X86_FEATURE_LFENCE_RDTSC)
 
diff --git a/include/linux/list.h b/include/linux/list.h
index dd6c2041d09c..1a1b39fdd122 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -636,7 +636,8 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry(pos, head, member) \
   for (pos = list_first_entry(head, typeof(*pos), member); \
- !list_entry_is_head(pos, head, member); \
+ ({ bool _cond = !list_entry_is_head(pos, head, member); \
+ pos = select_nospec(_cond, pos, NULL); _cond; }); \
        pos = list_next_entry(pos, member))