tools/testing/radix-tree/regression2.c

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