There is no reason to maintain the list structure while freeing the debug elements. Aside from the redundant pointer manipulations, it is also inefficient from a locality-of-reference viewpoint, since they are visited in a random order (wrt. the order they were allocated). Furthermore, if we jumped to exit: after detecting list corruption, it is actually dangerous. So just free the elements in the order they were allocated, using the backing array elts. Allocate that using kcalloc(), so that if allocation of one of the debug element fails, we just end up calling kfree(NULL) for the trailing elements. Minor details: Use sizeof(*elts) instead of sizeof(void *), and return err immediately when allocation of elts fails, to avoid introducing another label just before the final return statement. Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com> Cc: Don Mullis <don.mullis@gmail.com> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
295 lines
7.1 KiB
C
295 lines
7.1 KiB
C
#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/list_sort.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#define MAX_LIST_LENGTH_BITS 20
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/*
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* Returns a list organized in an intermediate format suited
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* to chaining of merge() calls: null-terminated, no reserved or
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* sentinel head node, "prev" links not maintained.
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*/
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static struct list_head *merge(void *priv,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b),
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struct list_head *a, struct list_head *b)
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{
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struct list_head head, *tail = &head;
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while (a && b) {
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/* if equal, take 'a' -- important for sort stability */
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if ((*cmp)(priv, a, b) <= 0) {
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tail->next = a;
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a = a->next;
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} else {
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tail->next = b;
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b = b->next;
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}
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tail = tail->next;
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}
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tail->next = a?:b;
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return head.next;
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}
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/*
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* Combine final list merge with restoration of standard doubly-linked
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* list structure. This approach duplicates code from merge(), but
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* runs faster than the tidier alternatives of either a separate final
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* prev-link restoration pass, or maintaining the prev links
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* throughout.
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*/
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static void merge_and_restore_back_links(void *priv,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b),
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struct list_head *head,
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struct list_head *a, struct list_head *b)
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{
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struct list_head *tail = head;
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while (a && b) {
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/* if equal, take 'a' -- important for sort stability */
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if ((*cmp)(priv, a, b) <= 0) {
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tail->next = a;
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a->prev = tail;
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a = a->next;
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} else {
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tail->next = b;
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b->prev = tail;
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b = b->next;
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}
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tail = tail->next;
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}
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tail->next = a ? : b;
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do {
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/*
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* In worst cases this loop may run many iterations.
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* Continue callbacks to the client even though no
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* element comparison is needed, so the client's cmp()
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* routine can invoke cond_resched() periodically.
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*/
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(*cmp)(priv, tail->next, tail->next);
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tail->next->prev = tail;
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tail = tail->next;
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} while (tail->next);
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tail->next = head;
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head->prev = tail;
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}
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/**
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* list_sort - sort a list
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* @priv: private data, opaque to list_sort(), passed to @cmp
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* @head: the list to sort
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* @cmp: the elements comparison function
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*
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* This function implements "merge sort", which has O(nlog(n))
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* complexity.
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*
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* The comparison function @cmp must return a negative value if @a
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* should sort before @b, and a positive value if @a should sort after
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* @b. If @a and @b are equivalent, and their original relative
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* ordering is to be preserved, @cmp must return 0.
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*/
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void list_sort(void *priv, struct list_head *head,
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int (*cmp)(void *priv, struct list_head *a,
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struct list_head *b))
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{
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struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
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-- last slot is a sentinel */
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int lev; /* index into part[] */
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int max_lev = 0;
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struct list_head *list;
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if (list_empty(head))
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return;
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memset(part, 0, sizeof(part));
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head->prev->next = NULL;
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list = head->next;
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while (list) {
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struct list_head *cur = list;
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list = list->next;
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cur->next = NULL;
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for (lev = 0; part[lev]; lev++) {
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cur = merge(priv, cmp, part[lev], cur);
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part[lev] = NULL;
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}
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if (lev > max_lev) {
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if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
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printk_once(KERN_DEBUG "list passed to"
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" list_sort() too long for"
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" efficiency\n");
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lev--;
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}
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max_lev = lev;
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}
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part[lev] = cur;
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}
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for (lev = 0; lev < max_lev; lev++)
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if (part[lev])
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list = merge(priv, cmp, part[lev], list);
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merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
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}
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EXPORT_SYMBOL(list_sort);
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#ifdef CONFIG_TEST_LIST_SORT
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#include <linux/random.h>
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/*
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* The pattern of set bits in the list length determines which cases
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* are hit in list_sort().
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*/
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#define TEST_LIST_LEN (512+128+2) /* not including head */
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#define TEST_POISON1 0xDEADBEEF
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#define TEST_POISON2 0xA324354C
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struct debug_el {
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unsigned int poison1;
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struct list_head list;
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unsigned int poison2;
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int value;
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unsigned serial;
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};
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/* Array, containing pointers to all elements in the test list */
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static struct debug_el **elts __initdata;
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static int __init check(struct debug_el *ela, struct debug_el *elb)
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{
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if (ela->serial >= TEST_LIST_LEN) {
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printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
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ela->serial);
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return -EINVAL;
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}
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if (elb->serial >= TEST_LIST_LEN) {
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printk(KERN_ERR "list_sort_test: error: incorrect serial %d\n",
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elb->serial);
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return -EINVAL;
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}
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if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
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printk(KERN_ERR "list_sort_test: error: phantom element\n");
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return -EINVAL;
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}
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if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
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printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
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ela->poison1, ela->poison2);
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return -EINVAL;
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}
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if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
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printk(KERN_ERR "list_sort_test: error: bad poison: %#x/%#x\n",
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elb->poison1, elb->poison2);
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return -EINVAL;
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}
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return 0;
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}
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static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
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{
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struct debug_el *ela, *elb;
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ela = container_of(a, struct debug_el, list);
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elb = container_of(b, struct debug_el, list);
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check(ela, elb);
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return ela->value - elb->value;
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}
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static int __init list_sort_test(void)
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{
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int i, count = 1, err = -ENOMEM;
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struct debug_el *el;
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struct list_head *cur;
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LIST_HEAD(head);
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printk(KERN_DEBUG "list_sort_test: start testing list_sort()\n");
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elts = kcalloc(TEST_LIST_LEN, sizeof(*elts), GFP_KERNEL);
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if (!elts) {
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printk(KERN_ERR "list_sort_test: error: cannot allocate "
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"memory\n");
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return err;
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}
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for (i = 0; i < TEST_LIST_LEN; i++) {
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el = kmalloc(sizeof(*el), GFP_KERNEL);
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if (!el) {
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printk(KERN_ERR "list_sort_test: error: cannot "
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"allocate memory\n");
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goto exit;
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}
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/* force some equivalencies */
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el->value = prandom_u32() % (TEST_LIST_LEN / 3);
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el->serial = i;
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el->poison1 = TEST_POISON1;
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el->poison2 = TEST_POISON2;
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elts[i] = el;
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list_add_tail(&el->list, &head);
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}
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list_sort(NULL, &head, cmp);
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err = -EINVAL;
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for (cur = head.next; cur->next != &head; cur = cur->next) {
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struct debug_el *el1;
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int cmp_result;
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if (cur->next->prev != cur) {
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printk(KERN_ERR "list_sort_test: error: list is "
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"corrupted\n");
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goto exit;
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}
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cmp_result = cmp(NULL, cur, cur->next);
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if (cmp_result > 0) {
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printk(KERN_ERR "list_sort_test: error: list is not "
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"sorted\n");
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goto exit;
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}
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el = container_of(cur, struct debug_el, list);
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el1 = container_of(cur->next, struct debug_el, list);
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if (cmp_result == 0 && el->serial >= el1->serial) {
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printk(KERN_ERR "list_sort_test: error: order of "
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"equivalent elements not preserved\n");
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goto exit;
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}
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if (check(el, el1)) {
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printk(KERN_ERR "list_sort_test: error: element check "
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"failed\n");
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goto exit;
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}
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count++;
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}
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if (head.prev != cur) {
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printk(KERN_ERR "list_sort_test: error: list is corrupted\n");
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goto exit;
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}
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if (count != TEST_LIST_LEN) {
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printk(KERN_ERR "list_sort_test: error: bad list length %d",
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count);
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goto exit;
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}
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err = 0;
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exit:
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for (i = 0; i < TEST_LIST_LEN; i++)
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kfree(elts[i]);
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kfree(elts);
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return err;
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}
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module_init(list_sort_test);
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#endif /* CONFIG_TEST_LIST_SORT */
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