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Subject[PATCH RFC tip/core/rcu 03/30] rculist: avoid __rcu annotations
Date
From: Arnd Bergmann <arnd@arndb.de>

This avoids warnings from missing __rcu annotations
in the rculist implementation, making it possible to
use the same lists in both RCU and non-RCU cases.

We can add rculist annotations later, together with
lockdep support for rculist, which is missing as well,
but that may involve changing all the users.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
include/linux/rculist.h | 53 ++++++++++++++++++++++++++--------------
include/linux/rculist_nulls.h | 16 ++++++++----
kernel/pid.c | 2 +-
3 files changed, 46 insertions(+), 25 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4ec3b38..c10b105 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -10,6 +10,12 @@
#include <linux/rcupdate.h>

/*
+ * 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
@@ -20,7 +26,7 @@ static inline void __list_add_rcu(struct list_head *new,
{
new->next = next;
new->prev = prev;
- rcu_assign_pointer(prev->next, new);
+ rcu_assign_pointer(list_next_rcu(prev), new);
next->prev = new;
}

@@ -138,7 +144,7 @@ static inline void list_replace_rcu(struct list_head *old,
{
new->next = old->next;
new->prev = old->prev;
- rcu_assign_pointer(new->prev->next, new);
+ rcu_assign_pointer(list_next_rcu(new->prev), new);
new->next->prev = new;
old->prev = LIST_POISON2;
}
@@ -193,7 +199,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
*/

last->next = at;
- rcu_assign_pointer(head->next, first);
+ rcu_assign_pointer(list_next_rcu(head), first);
first->prev = head;
at->prev = last;
}
@@ -208,7 +214,9 @@ static inline void list_splice_init_rcu(struct list_head *list,
* 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(rcu_dereference_raw(ptr), type, member)
+ ({typeof (*ptr) __rcu *__ptr = (typeof (*ptr) __rcu __force *)ptr; \
+ container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
+ })

/**
* list_first_entry_rcu - get the first element from a list
@@ -225,9 +233,9 @@ static inline void list_splice_init_rcu(struct list_head *list,
list_entry_rcu((ptr)->next, type, member)

#define __list_for_each_rcu(pos, head) \
- for (pos = rcu_dereference_raw((head)->next); \
+ for (pos = rcu_dereference_raw(list_next_rcu(head)); \
pos != (head); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_raw(list_next_rcu((pos)))

/**
* list_for_each_entry_rcu - iterate over rcu list of given type
@@ -257,9 +265,9 @@ static inline void list_splice_init_rcu(struct list_head *list,
* as long as the traversal is guarded by rcu_read_lock().
*/
#define list_for_each_continue_rcu(pos, head) \
- for ((pos) = rcu_dereference_raw((pos)->next); \
+ for ((pos) = rcu_dereference_raw(list_next_rcu(pos)); \
prefetch((pos)->next), (pos) != (head); \
- (pos) = rcu_dereference_raw((pos)->next))
+ (pos) = rcu_dereference_raw(list_next_rcu(pos)))

/**
* list_for_each_entry_continue_rcu - continue iteration over list of given type
@@ -314,12 +322,19 @@ static inline void hlist_replace_rcu(struct hlist_node *old,

new->next = next;
new->pprev = old->pprev;
- rcu_assign_pointer(*new->pprev, new);
+ 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.
@@ -346,7 +361,7 @@ static inline void hlist_add_head_rcu(struct hlist_node *n,

n->next = first;
n->pprev = &h->first;
- rcu_assign_pointer(h->first, n);
+ rcu_assign_pointer(hlist_first_rcu(h), n);
if (first)
first->pprev = &n->next;
}
@@ -374,7 +389,7 @@ static inline void hlist_add_before_rcu(struct hlist_node *n,
{
n->pprev = next->pprev;
n->next = next;
- rcu_assign_pointer(*(n->pprev), n);
+ rcu_assign_pointer(hlist_pprev_rcu(n), n);
next->pprev = &n->next;
}

@@ -401,15 +416,15 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev,
{
n->next = prev->next;
n->pprev = &prev->next;
- rcu_assign_pointer(prev->next, n);
+ 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((head)->first); \
- pos && ({ prefetch(pos->next); 1; }); \
- pos = rcu_dereference(pos->next))
+#define __hlist_for_each_rcu(pos, head) \
+ for (pos = rcu_dereference(hlist_first_rcu(head)); \
+ pos && ({ prefetch(pos->next); 1; }); \
+ pos = rcu_dereference(hlist_next_rcu(pos)))

/**
* hlist_for_each_entry_rcu - iterate over rcu list of given type
@@ -422,11 +437,11 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev,
* 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(tpos, pos, head, member) \
- for (pos = rcu_dereference_raw((head)->first); \
+#define hlist_for_each_entry_rcu(tpos, pos, head, member) \
+ for (pos = rcu_dereference_raw(hlist_first_rcu(head)); \
pos && ({ prefetch(pos->next); 1; }) && \
({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_raw(hlist_next_rcu(pos)))

/**
* hlist_for_each_entry_rcu_bh - iterate over rcu list of given type
diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index b70ffe5..2ae1371 100644
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -37,6 +37,12 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
}
}

+#define hlist_nulls_first_rcu(head) \
+ (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
+
+#define hlist_nulls_next_rcu(node) \
+ (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
+
/**
* hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
* @n: the element to delete from the hash list.
@@ -88,7 +94,7 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,

n->next = first;
n->pprev = &h->first;
- rcu_assign_pointer(h->first, n);
+ rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
if (!is_a_nulls(first))
first->pprev = &n->next;
}
@@ -100,11 +106,11 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
* @member: the name of the hlist_nulls_node within the struct.
*
*/
-#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
- for (pos = rcu_dereference_raw((head)->first); \
- (!is_a_nulls(pos)) && \
+#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
+ for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
+ (!is_a_nulls(pos)) && \
({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
- pos = rcu_dereference_raw(pos->next))
+ pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))

#endif
#endif
diff --git a/kernel/pid.c b/kernel/pid.c
index e9fd8c1..28e8ce4 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -367,7 +367,7 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type)
struct task_struct *result = NULL;
if (pid) {
struct hlist_node *first;
- first = rcu_dereference_check(pid->tasks[type].first,
+ first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
rcu_read_lock_held() ||
lockdep_tasklist_lock_is_held());
if (first)
--
1.7.0.6


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