From: Nick Piggin <npiggin@xxxxxxx>
Introduce a type of hlist that can support the use of the lowest bit
in the hlist_head. This will be subsequently used to implement
per-bucket bit spinlock for inode hashes.
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
include/linux/list_bl.h | 127 +++++++++++++++++++++++++++++++++++++++++++
include/linux/rculist_bl.h | 128 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 255 insertions(+), 0 deletions(-)
create mode 100644 include/linux/list_bl.h
create mode 100644 include/linux/rculist_bl.h
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
new file mode 100644
index 0000000..cf8acfc
--- /dev/null
+++ b/include/linux/list_bl.h
@@ -0,0 +1,127 @@
+#ifndef _LINUX_LIST_BL_H
+#define _LINUX_LIST_BL_H
+
+#include <linux/list.h>
+#include <linux/bit_spinlock.h>
+
+/*
+ * Special version of lists, where head of the list has a bit spinlock
+ * in the lowest bit. This is useful for scalable hash tables without
+ * increasing memory footprint overhead.
+ *
+ * For modification operations, the 0 bit of hlist_bl_head->first
+ * pointer must be set.
+ */
+
+#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
+#define LIST_BL_LOCKMASK 1UL
+#else
+#define LIST_BL_LOCKMASK 0UL
+#endif
+
+#ifdef CONFIG_DEBUG_LIST
+#define LIST_BL_BUG_ON(x) BUG_ON(x)
+#else
+#define LIST_BL_BUG_ON(x)
+#endif
+
+
+struct hlist_bl_head {
+ struct hlist_bl_node *first;
+};
+
+struct hlist_bl_node {
+ struct hlist_bl_node *next, **pprev;
+};
+#define INIT_HLIST_BL_HEAD(ptr) \
+ ((ptr)->first = NULL)
+
+static inline void INIT_HLIST_BL_NODE(struct hlist_bl_node *h)
+{
+ h->next = NULL;
+ h->pprev = NULL;
+}
+
+#define hlist_bl_entry(ptr, type, member) container_of(ptr,type,member)
+
+static inline int hlist_bl_unhashed(const struct hlist_bl_node *h)
+{
+ return !h->pprev;
+}
+
+static inline struct hlist_bl_node *hlist_bl_first(struct hlist_bl_head *h)
+{
+ return (struct hlist_bl_node *)
+ ((unsigned long)h->first & ~LIST_BL_LOCKMASK);
+}
+
+static inline void hlist_bl_set_first(struct hlist_bl_head *h,
+ struct hlist_bl_node *n)
+{
+ LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
+ LIST_BL_BUG_ON(!bit_spin_is_locked(0, (unsigned long *)&h->first));
+ h->first = (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK);
+}
+
+static inline int hlist_bl_empty(const struct hlist_bl_head *h)
+{
+ return !((unsigned long)h->first & ~LIST_BL_LOCKMASK);
+}
+
+static inline void hlist_bl_add_head(struct hlist_bl_node *n,
+ struct hlist_bl_head *h)
+{
+ struct hlist_bl_node *first = hlist_bl_first(h);
+
+ n->next = first;
+ if (first)
+ first->pprev = &n->next;
+ n->pprev = &h->first;
+ hlist_bl_set_first(h, n);
+}
+
+static inline void __hlist_bl_del(struct hlist_bl_node *n)
+{
+ struct hlist_bl_node *next = n->next;
+ struct hlist_bl_node **pprev = n->pprev;
+
+ LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
+
+ /* pprev may be `first`, so be careful not to lose the lock bit */
+ *pprev = (struct hlist_bl_node *)
+ ((unsigned long)next |
+ ((unsigned long)*pprev & LIST_BL_LOCKMASK));
+ if (next)
+ next->pprev = pprev;
+}
+
+static inline void hlist_bl_del(struct hlist_bl_node *n)
+{
+ __hlist_bl_del(n);
+ n->next = LIST_POISON1;
+ n->pprev = LIST_POISON2;
+}
+
+static inline void hlist_bl_del_init(struct hlist_bl_node *n)
+{
+ if (!hlist_bl_unhashed(n)) {
+ __hlist_bl_del(n);
+ INIT_HLIST_BL_NODE(n);
+ }
+}
+
+/**
+ * hlist_bl_for_each_entry - iterate over list of given type
+ * @tpos: the type * to use as a loop cursor.
+ * @pos: the &struct hlist_node to use as a loop cursor.
+ * @head: the head for your list.
+ * @member: the name of the hlist_node within the struct.
+ *
+ */
+#define hlist_bl_for_each_entry(tpos, pos, head, member) \
+ for (pos = hlist_bl_first(head); \
+ pos && \
+ ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1;}); \
+ pos = pos->next)
+
+#endif
diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
new file mode 100644
index 0000000..cdfb54e
--- /dev/null
+++ b/include/linux/rculist_bl.h
@@ -0,0 +1,128 @@
+#ifndef _LINUX_RCULIST_BL_H
+#define _LINUX_RCULIST_BL_H
+
+/*
+ * RCU-protected bl list version. See include/linux/list_bl.h.
+ */
+#include <linux/list_bl.h>
+#include <linux/rcupdate.h>
+#include <linux/bit_spinlock.h>
+
+static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
+ struct hlist_bl_node *n)
+{
+ LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
+ LIST_BL_BUG_ON(!bit_spin_is_locked(0, (unsigned long *)&h->first));
+ rcu_assign_pointer(h->first,
+ (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
+}
+
+static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
+{
+ return (struct hlist_bl_node *)
+ ((unsigned long)rcu_dereference(h->first) & ~LIST_BL_LOCKMASK);
+}
+
+/**
+ * hlist_bl_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: hlist_bl_unhashed() on the node returns 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_bl_add_head_rcu() or
+ * hlist_bl_del_rcu(), running on this same list. However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_bl_for_each_entry_rcu().
+ */
+static inline void hlist_bl_del_init_rcu(struct hlist_bl_node *n)
+{
+ if (!hlist_bl_unhashed(n)) {
+ __hlist_bl_del(n);
+ n->pprev = NULL;
+ }
+}
+
+/**
+ * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: hlist_bl_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_bl_add_head_rcu()
+ * or hlist_bl_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_bl_for_each_entry().
+ */
+static inline void hlist_bl_del_rcu(struct hlist_bl_node *n)
+{
+ __hlist_bl_del(n);
+ n->pprev = LIST_POISON2;
+}
+
+/**
+ * hlist_bl_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_bl,
+ * 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_bl_add_head_rcu()
+ * or hlist_bl_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_bl_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_bl_add_head_rcu(struct hlist_bl_node *n,
+ struct hlist_bl_head *h)
+{
+ struct hlist_bl_node *first;
+
+ /* don't need hlist_bl_first_rcu because we're under lock */
+ first = hlist_bl_first(h);
+
+ n->next = first;
+ if (first)
+ first->pprev = &n->next;
+ n->pprev = &h->first;
+
+ /* need _rcu because we can have concurrent lock free readers */
+ hlist_bl_set_first_rcu(h, n);
+}
+/**
+ * hlist_bl_for_each_entry_rcu - iterate over rcu list of given type
+ * @tpos: the type * to use as a loop cursor.
+ * @pos: the &struct hlist_bl_node to use as a loop cursor.
+ * @head: the head for your list.
+ * @member: the name of the hlist_bl_node within the struct.
+ *
+ */
+#define hlist_bl_for_each_entry_rcu(tpos, pos, head, member) \
+ for (pos = hlist_bl_first_rcu(head); \
+ pos && \
+ ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
+ pos = rcu_dereference_raw(pos->next))
+
+#endif
--
1.6.5.2
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