Merge tag 'asm-generic-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[mirror_ubuntu-zesty-kernel.git] / include / linux / rculist.h

#ifndef _LINUX_RCULIST_H
#define _LINUX_RCULIST_H

#ifdef __KERNEL__

/*
 * RCU-protected list version
 */
#include <linux/list.h>
#include <linux/rcupdate.h>

/*
 * Why is there no list_empty_rcu()?  Because list_empty() serves this
 * purpose.  The list_empty() function fetches the RCU-protected pointer
 * and compares it to the address of the list head, but neither dereferences
 * this pointer itself nor provides this pointer to the caller.  Therefore,
 * it is not necessary to use rcu_dereference(), so that list_empty() can
 * be used anywhere you would want to use a list_empty_rcu().
 */

/*
 * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
 * @list: list to be initialized
 *
 * You should instead use INIT_LIST_HEAD() for normal initialization and
 * cleanup tasks, when readers have no access to the list being initialized.
 * However, if the list being initialized is visible to readers, you
 * need to keep the compiler from being too mischievous.
 */
static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
{
        WRITE_ONCE(list->next, list);
        WRITE_ONCE(list->prev, list);
}

/*
 * return the ->next pointer of a list_head in an rcu safe
 * way, we must not access it directly
 */
#define list_next_rcu(list)     (*((struct list_head __rcu **)(&(list)->next)))

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

/**
 * list_add_rcu - add a new entry to rcu-protected list
 * @new: new entry to be added
 * @head: list head to add it after
 *
 * Insert a new entry after the specified head.
 * This is good for implementing stacks.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_add_rcu()
 * or list_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 */
static inline void list_add_rcu(struct list_head *new, struct list_head *head)
{
        __list_add_rcu(new, head, head->next);
}

/**
 * list_add_tail_rcu - add a new entry to rcu-protected list
 * @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.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_add_tail_rcu()
 * or list_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 */
static inline void list_add_tail_rcu(struct list_head *new,
                                        struct list_head *head)
{
        __list_add_rcu(new, head->prev, head);
}

/**
 * list_del_rcu - deletes entry from list without re-initialization
 * @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. It is useful for RCU based
 * lockfree traversal.
 *
 * In particular, it means that we can not poison the forward
 * pointers that may still be used for walking the list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_del_rcu()
 * or list_add_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 *
 * Note that the caller is not permitted to immediately free
 * the newly deleted entry.  Instead, either synchronize_rcu()
 * or call_rcu() must be used to defer freeing until an RCU
 * grace period has elapsed.
 */
static inline void list_del_rcu(struct list_head *entry)
{
        __list_del_entry(entry);
        entry->prev = LIST_POISON2;
}

/**
 * hlist_del_init_rcu - deletes entry from hash list with re-initialization
 * @n: the element to delete from the hash list.
 *
 * Note: list_unhashed() on the node return true after this. It is
 * useful for RCU based read lockfree traversal if the writer side
 * must know if the list entry is still hashed or already unhashed.
 *
 * In particular, it means that we can not poison the forward pointers
 * that may still be used for walking the hash list and we can only
 * zero the pprev pointer so list_unhashed() will return true after
 * this.
 *
 * The caller must take whatever precautions are necessary (such as
 * holding appropriate locks) to avoid racing with another
 * list-mutation primitive, such as hlist_add_head_rcu() or
 * hlist_del_rcu(), running on this same list.  However, it is
 * perfectly legal to run concurrently with the _rcu list-traversal
 * primitives, such as hlist_for_each_entry_rcu().
 */
static inline void hlist_del_init_rcu(struct hlist_node *n)
{
        if (!hlist_unhashed(n)) {
                __hlist_del(n);
                n->pprev = NULL;
        }
}

/**
 * list_replace_rcu - replace old entry by new one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * The @old entry will be replaced with the @new entry atomically.
 * Note: @old should not be empty.
 */
static inline void list_replace_rcu(struct list_head *old,
                                struct list_head *new)
{
        new->next = old->next;
        new->prev = old->prev;
        rcu_assign_pointer(list_next_rcu(new->prev), new);
        new->next->prev = new;
        old->prev = LIST_POISON2;
}

/**
 * list_splice_init_rcu - splice an RCU-protected list into an existing list.
 * @list:       the RCU-protected list to splice
 * @head:       the place in the list to splice the first list into
 * @sync:       function to sync: synchronize_rcu(), synchronize_sched(), ...
 *
 * @head can be RCU-read traversed concurrently with this function.
 *
 * Note that this function blocks.
 *
 * Important note: the caller must take whatever action is necessary to
 *      prevent any other updates to @head.  In principle, it is possible
 *      to modify the list as soon as sync() begins execution.
 *      If this sort of thing becomes necessary, an alternative version
 *      based on call_rcu() could be created.  But only if -really-
 *      needed -- there is no shortage of RCU API members.
 */
static inline void list_splice_init_rcu(struct list_head *list,
                                        struct list_head *head,
                                        void (*sync)(void))
{
        struct list_head *first = list->next;
        struct list_head *last = list->prev;
        struct list_head *at = head->next;

        if (list_empty(list))
                return;

        /*
         * "first" and "last" tracking list, so initialize it.  RCU readers
         * have access to this list, so we must use INIT_LIST_HEAD_RCU()
         * instead of INIT_LIST_HEAD().
         */

        INIT_LIST_HEAD_RCU(list);

        /*
         * At this point, the list body still points to the source list.
         * Wait for any readers to finish using the list before splicing
         * the list body into the new list.  Any new readers will see
         * an empty list.
         */

        sync();

        /*
         * Readers are finished with the source list, so perform splice.
         * The order is important if the new list is global and accessible
         * to concurrent RCU readers.  Note that RCU readers are not
         * permitted to traverse the prev pointers without excluding
         * this function.
         */

        last->next = at;
        rcu_assign_pointer(list_next_rcu(head), first);
        first->prev = head;
        at->prev = last;
}

/**
 * list_entry_rcu - 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.
 *
 * This primitive may safely run concurrently with the _rcu list-mutation
 * 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)

/**
 * Where are list_empty_rcu() and list_first_entry_rcu()?
 *
 * Implementing those functions following their counterparts list_empty() and
 * list_first_entry() is not advisable because they lead to subtle race
 * conditions as the following snippet shows:
 *
 * if (!list_empty_rcu(mylist)) {
 *      struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
 *      do_something(bar);
 * }
 *
 * The list may not be empty when list_empty_rcu checks it, but it may be when
 * list_first_entry_rcu rereads the ->next pointer.
 *
 * Rereading the ->next pointer is not a problem for list_empty() and
 * list_first_entry() because they would be protected by a lock that blocks
 * writers.
 *
 * See list_first_or_null_rcu for an alternative.
 */

/**
 * list_first_or_null_rcu - get the first element from a list
 * @ptr:        the list head to take the element from.
 * @type:       the type of the struct this is embedded in.
 * @member:     the name of the list_head within the struct.
 *
 * Note that if the list is empty, it returns NULL.
 *
 * This primitive may safely run concurrently with the _rcu list-mutation
 * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
 */
#define list_first_or_null_rcu(ptr, type, member) \
({ \
        struct list_head *__ptr = (ptr); \
        struct list_head *__next = READ_ONCE(__ptr->next); \
        likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
})

/**
 * list_for_each_entry_rcu      -       iterate over rcu 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.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_entry_rcu(pos, head, member) \
        for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
                &pos->member != (head); \
                pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

/**
 * list_for_each_entry_continue_rcu - continue iteration 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.
 *
 * Continue to iterate over list of given type, continuing after
 * the current position.
 */
#define list_for_each_entry_continue_rcu(pos, head, member)             \
        for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
             &pos->member != (head);    \
             pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

/**
 * hlist_del_rcu - deletes entry from hash list without re-initialization
 * @n: the element to delete from the hash list.
 *
 * Note: list_unhashed() on entry does not return true after this,
 * the entry is in an undefined state. It is useful for RCU based
 * lockfree traversal.
 *
 * In particular, it means that we can not poison the forward
 * pointers that may still be used for walking the hash list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry().
 */
static inline void hlist_del_rcu(struct hlist_node *n)
{
        __hlist_del(n);
        n->pprev = LIST_POISON2;
}

/**
 * hlist_replace_rcu - replace old entry by new one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * The @old entry will be replaced with the @new entry atomically.
 */
static inline void hlist_replace_rcu(struct hlist_node *old,
                                        struct hlist_node *new)
{
        struct hlist_node *next = old->next;

        new->next = next;
        new->pprev = old->pprev;
        rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new);
        if (next)
                new->next->pprev = &new->next;
        old->pprev = LIST_POISON2;
}

/*
 * return the first or the next element in an RCU protected hlist
 */
#define hlist_first_rcu(head)   (*((struct hlist_node __rcu **)(&(head)->first)))
#define hlist_next_rcu(node)    (*((struct hlist_node __rcu **)(&(node)->next)))
#define hlist_pprev_rcu(node)   (*((struct hlist_node __rcu **)((node)->pprev)))

/**
 * hlist_add_head_rcu
 * @n: the element to add to the hash list.
 * @h: the list to add to.
 *
 * Description:
 * Adds the specified element to the specified hlist,
 * while permitting racing traversals.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.  Regardless of the type of CPU, the
 * list-traversal primitive must be guarded by rcu_read_lock().
 */
static inline void hlist_add_head_rcu(struct hlist_node *n,
                                        struct hlist_head *h)
{
        struct hlist_node *first = h->first;

        n->next = first;
        n->pprev = &h->first;
        rcu_assign_pointer(hlist_first_rcu(h), n);
        if (first)
                first->pprev = &n->next;
}

/**
 * hlist_add_before_rcu
 * @n: the new element to add to the hash list.
 * @next: the existing element to add the new element before.
 *
 * Description:
 * Adds the specified element to the specified hlist
 * before the specified node while permitting racing traversals.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.
 */
static inline void hlist_add_before_rcu(struct hlist_node *n,
                                        struct hlist_node *next)
{
        n->pprev = next->pprev;
        n->next = next;
        rcu_assign_pointer(hlist_pprev_rcu(n), n);
        next->pprev = &n->next;
}

/**
 * hlist_add_behind_rcu
 * @n: the new element to add to the hash list.
 * @prev: the existing element to add the new element after.
 *
 * Description:
 * Adds the specified element to the specified hlist
 * after the specified node while permitting racing traversals.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.
 */
static inline void hlist_add_behind_rcu(struct hlist_node *n,
                                        struct hlist_node *prev)
{
        n->next = prev->next;
        n->pprev = &prev->next;
        rcu_assign_pointer(hlist_next_rcu(prev), n);
        if (n->next)
                n->next->pprev = &n->next;
}

#define __hlist_for_each_rcu(pos, head)                         \
        for (pos = rcu_dereference(hlist_first_rcu(head));      \
             pos;                                               \
             pos = rcu_dereference(hlist_next_rcu(pos)))

/**
 * hlist_for_each_entry_rcu - iterate over rcu list of given type
 * @pos:        the type * to use as a loop cursor.
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define hlist_for_each_entry_rcu(pos, head, member)                     \
        for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
                        typeof(*(pos)), member);                        \
                pos;                                                    \
                pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
                        &(pos)->member)), typeof(*(pos)), member))

/**
 * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
 * @pos:        the type * to use as a loop cursor.
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 *
 * This is the same as hlist_for_each_entry_rcu() except that it does
 * not do any RCU debugging or tracing.
 */
#define hlist_for_each_entry_rcu_notrace(pos, head, member)                     \
        for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
                        typeof(*(pos)), member);                        \
                pos;                                                    \
                pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
                        &(pos)->member)), typeof(*(pos)), member))

/**
 * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
 * @pos:        the type * to use as a loop cursor.
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define hlist_for_each_entry_rcu_bh(pos, head, member)                  \
        for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
                        typeof(*(pos)), member);                        \
                pos;                                                    \
                pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
                        &(pos)->member)), typeof(*(pos)), member))

/**
 * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point
 * @pos:        the type * to use as a loop cursor.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue_rcu(pos, member)                  \
        for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
                        &(pos)->member)), typeof(*(pos)), member);      \
             pos;                                                       \
             pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
                        &(pos)->member)), typeof(*(pos)), member))

/**
 * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point
 * @pos:        the type * to use as a loop cursor.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue_rcu_bh(pos, member)               \
        for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(  \
                        &(pos)->member)), typeof(*(pos)), member);      \
             pos;                                                       \
             pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(  \
                        &(pos)->member)), typeof(*(pos)), member))

/**
 * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point
 * @pos:        the type * to use as a loop cursor.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_from_rcu(pos, member)                      \
        for (; pos;                                                     \
             pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
                        &(pos)->member)), typeof(*(pos)), member))

#endif  /* __KERNEL__ */
#endif