1 files changed, 262 insertions, 73 deletions

diff --git a/lib/list_sort.c b/lib/list_sort.c
index 19d11e0bb95..1183fa70a44 100644
--- a/lib/list_sort.c
+++ b/lib/list_sort.c
@@ -4,99 +4,288 @@
 #include <linux/slab.h>
 #include <linux/list.h>
 
+#define MAX_LIST_LENGTH_BITS 20
+
+/*
+ * Returns a list organized in an intermediate format suited
+ * to chaining of merge() calls: null-terminated, no reserved or
+ * sentinel head node, "prev" links not maintained.
+ */
+static struct list_head *merge(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				struct list_head *a, struct list_head *b)
+{
+	struct list_head head, *tail = &head;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(priv, a, b) <= 0) {
+			tail->next = a;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a?:b;
+	return head.next;
+}
+
+/*
+ * Combine final list merge with restoration of standard doubly-linked
+ * list structure.  This approach duplicates code from merge(), but
+ * runs faster than the tidier alternatives of either a separate final
+ * prev-link restoration pass, or maintaining the prev links
+ * throughout.
+ */
+static void merge_and_restore_back_links(void *priv,
+				int (*cmp)(void *priv, struct list_head *a,
+					struct list_head *b),
+				struct list_head *head,
+				struct list_head *a, struct list_head *b)
+{
+	struct list_head *tail = head;
+
+	while (a && b) {
+		/* if equal, take 'a' -- important for sort stability */
+		if ((*cmp)(priv, a, b) <= 0) {
+			tail->next = a;
+			a->prev = tail;
+			a = a->next;
+		} else {
+			tail->next = b;
+			b->prev = tail;
+			b = b->next;
+		}
+		tail = tail->next;
+	}
+	tail->next = a ? : b;
+
+	do {
+		/*
+		 * In worst cases this loop may run many iterations.
+		 * Continue callbacks to the client even though no
+		 * element comparison is needed, so the client's cmp()
+		 * routine can invoke cond_resched() periodically.
+		 */
+		(*cmp)(priv, tail->next, tail->next);
+
+		tail->next->prev = tail;
+		tail = tail->next;
+	} while (tail->next);
+
+	tail->next = head;
+	head->prev = tail;
+}
+
 /**
- * list_sort - sort a list.
- * @priv: private data, passed to @cmp
+ * list_sort - sort a list
+ * @priv: private data, opaque to list_sort(), passed to @cmp
  * @head: the list to sort
  * @cmp: the elements comparison function
  *
- * This function has been implemented by Mark J Roberts <mjr@znex.org>. It
- * implements "merge sort" which has O(nlog(n)) complexity. The list is sorted
- * in ascending order.
+ * This function implements "merge sort", which has O(nlog(n))
+ * complexity.
  *
- * The comparison function @cmp is supposed to return a negative value if @a is
- * less than @b, and a positive value if @a is greater than @b. If @a and @b
- * are equivalent, then it does not matter what this function returns.
+ * The comparison function @cmp must return a negative value if @a
+ * should sort before @b, and a positive value if @a should sort after
+ * @b. If @a and @b are equivalent, and their original relative
+ * ordering is to be preserved, @cmp must return 0.
  */
 void list_sort(void *priv, struct list_head *head,
-	       int (*cmp)(void *priv, struct list_head *a,
-			  struct list_head *b))
+		int (*cmp)(void *priv, struct list_head *a,
+			struct list_head *b))
 {
-	struct list_head *p, *q, *e, *list, *tail, *oldhead;
-	int insize, nmerges, psize, qsize, i;
+	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
+						-- last slot is a sentinel */
+	int lev;  /* index into part[] */
+	int max_lev = 0;
+	struct list_head *list;
 
 	if (list_empty(head))
 		return;
 
+	memset(part, 0, sizeof(part));
+
+	head->prev->next = NULL;
 	list = head->next;
-	list_del(head);
-	insize = 1;
-	for (;;) {
-		p = oldhead = list;
-		list = tail = NULL;
-		nmerges = 0;
-
-		while (p) {
-			nmerges++;
-			q = p;
-			psize = 0;
-			for (i = 0; i < insize; i++) {
-				psize++;
-				q = q->next == oldhead ? NULL : q->next;
-				if (!q)
-					break;
-			}
 
-			qsize = insize;
-			while (psize > 0 || (qsize > 0 && q)) {
-				if (!psize) {
-					e = q;
-					q = q->next;
-					qsize--;
-					if (q == oldhead)
-						q = NULL;
-				} else if (!qsize || !q) {
-					e = p;
-					p = p->next;
-					psize--;
-					if (p == oldhead)
-						p = NULL;
-				} else if (cmp(priv, p, q) <= 0) {
-					e = p;
-					p = p->next;
-					psize--;
-					if (p == oldhead)
-						p = NULL;
-				} else {
-					e = q;
-					q = q->next;
-					qsize--;
-					if (q == oldhead)
-						q = NULL;
-				}
-				if (tail)
-					tail->next = e;
-				else
-					list = e;
-				e->prev = tail;
-				tail = e;
+	while (list) {
+		struct list_head *cur = list;
+		list = list->next;
+		cur->next = NULL;
+
+		for (lev = 0; part[lev]; lev++) {
+			cur = merge(priv, cmp, part[lev], cur);
+			part[lev] = NULL;
+		}
+		if (lev > max_lev) {
+			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
+				printk_once(KERN_DEBUG "list passed to"
+					" list_sort() too long for"
+					" efficiency\n");
+				lev--;
 			}
-			p = q;
+			max_lev = lev;
 		}
+		part[lev] = cur;
+	}
+
+	for (lev = 0; lev < max_lev; lev++)
+		if (part[lev])
+			list = merge(priv, cmp, part[lev], list);
+
+	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
+}
+EXPORT_SYMBOL(list_sort);
+
+#ifdef CONFIG_TEST_LIST_SORT
+
+#include <linux/random.h>
 
-		tail->next = list;
-		list->prev = tail;
+/*
+ * The pattern of set bits in the list length determines which cases
+ * are hit in list_sort().
+ */
+#define TEST_LIST_LEN (512+128+2) /* not including head */
+
+#define TEST_POISON1 0xDEADBEEF
+#define TEST_POISON2 0xA324354C
 
-		if (nmerges <= 1)
-			break;
+struct debug_el {
+	unsigned int poison1;
+	struct list_head list;
+	unsigned int poison2;
+	int value;
+	unsigned serial;
+};
 
-		insize *= 2;
+/* Array, containing pointers to all elements in the test list */
+static struct debug_el **elts __initdata;
+
+static int __init check(struct debug_el *ela, struct debug_el *elb)
+{
+	if (ela->serial >= TEST_LIST_LEN) {
+		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
+				ela->serial);
+		return -EINVAL;
 	}
+	if (elb->serial >= TEST_LIST_LEN) {
+		printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
+				elb->serial);
+		return -EINVAL;
+	}
+	if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
+		printk(KERN_ERR "list_sort_test: error: phantom element\n");
+		return -EINVAL;
+	}
+	if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
+		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
+				ela->poison1, ela->poison2);
+		return -EINVAL;
+	}
+	if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
+		printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
+				elb->poison1, elb->poison2);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct debug_el *ela, *elb;
+
+	ela = container_of(a, struct debug_el, list);
+	elb = container_of(b, struct debug_el, list);
 
-	head->next = list;
-	head->prev = list->prev;
-	list->prev->next = head;
-	list->prev = head;
+	check(ela, elb);
+	return ela->value - elb->value;
 }
 
-EXPORT_SYMBOL(list_sort);
+static int __init list_sort_test(void)
+{
+	int i, count = 1, err = -EINVAL;
+	struct debug_el *el;
+	struct list_head *cur, *tmp;
+	LIST_HEAD(head);
+
+	printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
+
+	elts = kmalloc(sizeof(void *) * TEST_LIST_LEN, GFP_KERNEL);
+	if (!elts) {
+		printk(KERN_ERR "list_sort_test: error: cannot allocate "
+				"memory\n");
+		goto exit;
+	}
+
+	for (i = 0; i < TEST_LIST_LEN; i++) {
+		el = kmalloc(sizeof(*el), GFP_KERNEL);
+		if (!el) {
+			printk(KERN_ERR "list_sort_test: error: cannot "
+					"allocate memory\n");
+			goto exit;
+		}
+		 /* force some equivalencies */
+		el->value = prandom_u32() % (TEST_LIST_LEN / 3);
+		el->serial = i;
+		el->poison1 = TEST_POISON1;
+		el->poison2 = TEST_POISON2;
+		elts[i] = el;
+		list_add_tail(&el->list, &head);
+	}
+
+	list_sort(NULL, &head, cmp);
+
+	for (cur = head.next; cur->next != &head; cur = cur->next) {
+		struct debug_el *el1;
+		int cmp_result;
+
+		if (cur->next->prev != cur) {
+			printk(KERN_ERR "list_sort_test: error: list is "
+					"corrupted\n");
+			goto exit;
+		}
+
+		cmp_result = cmp(NULL, cur, cur->next);
+		if (cmp_result > 0) {
+			printk(KERN_ERR "list_sort_test: error: list is not "
+					"sorted\n");
+			goto exit;
+		}
+
+		el = container_of(cur, struct debug_el, list);
+		el1 = container_of(cur->next, struct debug_el, list);
+		if (cmp_result == 0 && el->serial >= el1->serial) {
+			printk(KERN_ERR "list_sort_test: error: order of "
+					"equivalent elements not preserved\n");
+			goto exit;
+		}
+
+		if (check(el, el1)) {
+			printk(KERN_ERR "list_sort_test: error: element check "
+					"failed\n");
+			goto exit;
+		}
+		count++;
+	}
+
+	if (count != TEST_LIST_LEN) {
+		printk(KERN_ERR "list_sort_test: error: bad list length %d",
+				count);
+		goto exit;
+	}
+
+	err = 0;
+exit:
+	kfree(elts);
+	list_for_each_safe(cur, tmp, &head) {
+		list_del(cur);
+		kfree(container_of(cur, struct debug_el, list));
+	}
+	return err;
+}
+module_init(list_sort_test);
+#endif /* CONFIG_TEST_LIST_SORT */