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// SPDX-License-Identifier: GPL-2.0
/*
* Regression2
* Description:
* Toshiyuki Okajima describes the following radix-tree bug:
*
* In the following case, we can get a hangup on
* radix_radix_tree_gang_lookup_tag_slot.
*
* 0. The radix tree contains RADIX_TREE_MAP_SIZE items. And the tag of
* a certain item has PAGECACHE_TAG_DIRTY.
* 1. radix_tree_range_tag_if_tagged(, start, end, , PAGECACHE_TAG_DIRTY,
* PAGECACHE_TAG_TOWRITE) is called to add PAGECACHE_TAG_TOWRITE tag
* for the tag which has PAGECACHE_TAG_DIRTY. However, there is no tag with
* PAGECACHE_TAG_DIRTY within the range from start to end. As the result,
* There is no tag with PAGECACHE_TAG_TOWRITE but the root tag has
* PAGECACHE_TAG_TOWRITE.
* 2. An item is added into the radix tree and then the level of it is
* extended into 2 from 1. At that time, the new radix tree node succeeds
* the tag status of the root tag. Therefore the tag of the new radix tree
* node has PAGECACHE_TAG_TOWRITE but there is not slot with
* PAGECACHE_TAG_TOWRITE tag in the child node of the new radix tree node.
* 3. The tag of a certain item is cleared with PAGECACHE_TAG_DIRTY.
* 4. All items within the index range from 0 to RADIX_TREE_MAP_SIZE - 1 are
* released. (Only the item which index is RADIX_TREE_MAP_SIZE exist in the
* radix tree.) As the result, the slot of the radix tree node is NULL but
* the tag which corresponds to the slot has PAGECACHE_TAG_TOWRITE.
* 5. radix_tree_gang_lookup_tag_slot(PAGECACHE_TAG_TOWRITE) calls
* __lookup_tag. __lookup_tag returns with 0. And __lookup_tag doesn't
* change the index that is the input and output parameter. Because the 1st
* slot of the radix tree node is NULL, but the tag which corresponds to
* the slot has PAGECACHE_TAG_TOWRITE.
* Therefore radix_tree_gang_lookup_tag_slot tries to get some items by
* calling __lookup_tag, but it cannot get any items forever.
*
* The fix is to change that radix_tree_tag_if_tagged doesn't tag the root tag
* if it doesn't set any tags within the specified range.
*
* Running:
* This test should run to completion immediately. The above bug would cause it
* to hang indefinitely.
*
* Upstream commit:
* Not yet
*/
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/slab.h>
#include <linux/radix-tree.h>
#include <stdlib.h>
#include <stdio.h>
#include "regression.h"
#include "test.h"
#define PAGECACHE_TAG_DIRTY 0
#define PAGECACHE_TAG_WRITEBACK 1
#define PAGECACHE_TAG_TOWRITE 2
static RADIX_TREE(mt_tree, GFP_KERNEL);
unsigned long page_count = 0;
struct page {
unsigned long index;
};
static struct page *page_alloc(void)
{
struct page *p;
p = malloc(sizeof(struct page));
p->index = page_count++;
return p;
}
void regression2_test(void)
{
int i;
struct page *p;
int max_slots = RADIX_TREE_MAP_SIZE;
unsigned long int start, end;
struct page *pages[1];
printv(1, "running regression test 2 (should take milliseconds)\n");
/* 0. */
for (i = 0; i <= max_slots - 1; i++) {
p = page_alloc();
radix_tree_insert(&mt_tree, i, p);
}
radix_tree_tag_set(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
/* 1. */
start = 0;
end = max_slots - 2;
tag_tagged_items(&mt_tree, NULL, start, end, 1,
PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
/* 2. */
p = page_alloc();
radix_tree_insert(&mt_tree, max_slots, p);
/* 3. */
radix_tree_tag_clear(&mt_tree, max_slots - 1, PAGECACHE_TAG_DIRTY);
/* 4. */
for (i = max_slots - 1; i >= 0; i--)
free(radix_tree_delete(&mt_tree, i));
/* 5. */
// NOTE: start should not be 0 because radix_tree_gang_lookup_tag_slot
// can return.
start = 1;
end = max_slots - 2;
radix_tree_gang_lookup_tag_slot(&mt_tree, (void ***)pages, start, end,
PAGECACHE_TAG_TOWRITE);
/* We remove all the remained nodes */
free(radix_tree_delete(&mt_tree, max_slots));
BUG_ON(!radix_tree_empty(&mt_tree));
printv(1, "regression test 2, done\n");
}
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