LXR linux/tools/testing/radix-tree/regression2.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Regression2
   4 * Description:
   5 * Toshiyuki Okajima describes the following radix-tree bug:
   6 *
   7 * In the following case, we can get a hangup on
   8 *   radix_radix_tree_gang_lookup_tag_slot.
   9 *
  10 * 0.  The radix tree contains RADIX_TREE_MAP_SIZE items. And the tag of
  11 *     a certain item has PAGECACHE_TAG_DIRTY.
  12 * 1.  radix_tree_range_tag_if_tagged(, start, end, , PAGECACHE_TAG_DIRTY,
  13 *     PAGECACHE_TAG_TOWRITE) is called to add PAGECACHE_TAG_TOWRITE tag
  14 *     for the tag which has PAGECACHE_TAG_DIRTY. However, there is no tag with
  15 *     PAGECACHE_TAG_DIRTY within the range from start to end. As the result,
  16 *     There is no tag with PAGECACHE_TAG_TOWRITE but the root tag has
  17 *     PAGECACHE_TAG_TOWRITE.
  18 * 2.  An item is added into the radix tree and then the level of it is
  19 *     extended into 2 from 1. At that time, the new radix tree node succeeds
  20 *     the tag status of the root tag. Therefore the tag of the new radix tree
  21 *     node has PAGECACHE_TAG_TOWRITE but there is not slot with
  22 *     PAGECACHE_TAG_TOWRITE tag in the child node of the new radix tree node.
  23 * 3.  The tag of a certain item is cleared with PAGECACHE_TAG_DIRTY.
  24 * 4.  All items within the index range from 0 to RADIX_TREE_MAP_SIZE - 1 are
  25 *     released. (Only the item which index is RADIX_TREE_MAP_SIZE exist in the
  26 *     radix tree.) As the result, the slot of the radix tree node is NULL but
  27 *     the tag which corresponds to the slot has PAGECACHE_TAG_TOWRITE.
  28 * 5.  radix_tree_gang_lookup_tag_slot(PAGECACHE_TAG_TOWRITE) calls
  29 *     __lookup_tag. __lookup_tag returns with 0. And __lookup_tag doesn't
  30 *     change the index that is the input and output parameter. Because the 1st
  31 *     slot of the radix tree node is NULL, but the tag which corresponds to
  32 *     the slot has PAGECACHE_TAG_TOWRITE.
  33 *     Therefore radix_tree_gang_lookup_tag_slot tries to get some items by
  34 *     calling __lookup_tag, but it cannot get any items forever.
  35 *
  36 * The fix is to change that radix_tree_tag_if_tagged doesn't tag the root tag
  37 * if it doesn't set any tags within the specified range.
  38 *
  39 * Running:
  40 * This test should run to completion immediately. The above bug would cause it
  41 * to hang indefinitely.
  42 *
  43 * Upstream commit:
  44 * Not yet
  45 */
  46#include <linux/kernel.h>
  47#include <linux/gfp.h>
  48#include <linux/slab.h>
  49#include <linux/radix-tree.h>
  50#include <stdlib.h>
  51#include <stdio.h>
  52
  53#include "regression.h"
  54#include "test.h"
  55
  56#define PAGECACHE_TAG_DIRTY     XA_MARK_0
  57#define PAGECACHE_TAG_WRITEBACK XA_MARK_1
  58#define PAGECACHE_TAG_TOWRITE   XA_MARK_2
  59
  60static RADIX_TREE(mt_tree, GFP_KERNEL);
  61unsigned long page_count = 0;
  62
  63struct page {
  64        unsigned long index;
  65};
  66
  67static struct page *page_alloc(void)
  68{
  69        struct page *p;
  70        p = malloc(sizeof(struct page));
  71        p->index = page_count++;
  72
  73        return p;
  74}
  75
  76void regression2_test(void)
  77{
  78        int i;
  79        struct page *p;
  80        int max_slots = RADIX_TREE_MAP_SIZE;
  81        unsigned long int start, end;
  82        struct page *pages[1];
  83
  84        printv(1, "running regression test 2 (should take milliseconds)\n");
  85        /* 0. */
  86        for (i = 0; i <= max_slots - 1; i++) {
  87                p = page_alloc();
  88                radix_tree_insert(&mt_tree, i, p);
  89        }
  90        radix_tree_tag_set(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
  91
  92        /* 1. */
  93        start = 0;
  94        end = max_slots - 2;
  95        tag_tagged_items(&mt_tree, start, end, 1,
  96                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
  97
  98        /* 2. */
  99        p = page_alloc();
 100        radix_tree_insert(&mt_tree, max_slots, p);
 101
 102        /* 3. */
 103        radix_tree_tag_clear(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
 104
 105        /* 4. */
 106        for (i = max_slots - 1; i >= 0; i--)
 107                free(radix_tree_delete(&mt_tree, i));
 108
 109        /* 5. */
 110        // NOTE: start should not be 0 because radix_tree_gang_lookup_tag_slot
 111        //       can return.
 112        start = 1;
 113        end = max_slots - 2;
 114        radix_tree_gang_lookup_tag_slot(&mt_tree, (void ***)pages, start, end,
 115                PAGECACHE_TAG_TOWRITE);
 116
 117        /* We remove all the remained nodes */
 118        free(radix_tree_delete(&mt_tree, max_slots));
 119
 120        BUG_ON(!radix_tree_empty(&mt_tree));
 121
 122        printv(1, "regression test 2, done\n");
 123}
 124