Commit eec48525 authored by Ross Zwisler's avatar Ross Zwisler Committed by Linus Torvalds

radix-tree tests: add iteration test

There are four cases I can see where we could end up with a NULL 'slot' in
radix_tree_next_slot().  This unit test exercises all four of them, making
sure that if in the future we have an unsafe path through
radix_tree_next_slot(), we'll catch it.

Here are details on the four cases:

1) radix_tree_iter_retry() via a non-tagged iteration like
radix_tree_for_each_slot().  In this case we currently aren't seeing a bug
because radix_tree_iter_retry() sets

    iter->next_index = iter->index;

which means that in in the else case in radix_tree_next_slot(), 'count' is
zero, so we skip over the while() loop and effectively just return NULL
without ever dereferencing 'slot'.

2) radix_tree_iter_retry() via tagged iteration like
radix_tree_for_each_tagged().  This case was giving us NULL pointer
dereferences in testing, and was fixed with this commit:

commit 3cb9185c ("radix-tree: fix radix_tree_iter_retry() for tagged
iterators.")

This fix doesn't explicitly check for 'slot' being NULL, though, it works
around the NULL pointer dereference by instead zeroing iter->tags in
radix_tree_iter_retry(), which makes us bail out of the if() case in
radix_tree_next_slot() before we dereference 'slot'.

3) radix_tree_iter_next() via via a non-tagged iteration like
radix_tree_for_each_slot().  This currently happens in shmem_tag_pins()
and shmem_partial_swap_usage().

As with non-tagged iteration, 'count' in the else case of
radix_tree_next_slot() is zero, so we skip over the while() loop and
effectively just return NULL without ever dereferencing 'slot'.

4) radix_tree_iter_next() via tagged iteration like
radix_tree_for_each_tagged().  This happens in shmem_wait_for_pins().

radix_tree_iter_next() zeros out iter->tags, so we end up exiting
radix_tree_next_slot() here:

    if (flags & RADIX_TREE_ITER_TAGGED) {
	    void *canon = slot;

	    iter->tags >>= 1;
	    if (unlikely(!iter->tags))
		    return NULL;

Link: http://lkml.kernel.org/r/20160815194237.25967-3-ross.zwisler@linux.intel.comSigned-off-by: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 915045fe
......@@ -3,7 +3,8 @@ CFLAGS += -I. -g -O2 -Wall -D_LGPL_SOURCE
LDFLAGS += -lpthread -lurcu
TARGETS = main
OFILES = main.o radix-tree.o linux.o test.o tag_check.o find_next_bit.o \
regression1.o regression2.o regression3.o multiorder.o
regression1.o regression2.o regression3.o multiorder.o \
iteration_check.o
targets: $(TARGETS)
......
/*
* iteration_check.c: test races having to do with radix tree iteration
* Copyright (c) 2016 Intel Corporation
* Author: Ross Zwisler <ross.zwisler@linux.intel.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*/
#include <linux/radix-tree.h>
#include <pthread.h>
#include "test.h"
#define NUM_THREADS 4
#define TAG 0
static pthread_mutex_t tree_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_t threads[NUM_THREADS];
RADIX_TREE(tree, GFP_KERNEL);
bool test_complete;
/* relentlessly fill the tree with tagged entries */
static void *add_entries_fn(void *arg)
{
int pgoff;
while (!test_complete) {
for (pgoff = 0; pgoff < 100; pgoff++) {
pthread_mutex_lock(&tree_lock);
if (item_insert(&tree, pgoff) == 0)
item_tag_set(&tree, pgoff, TAG);
pthread_mutex_unlock(&tree_lock);
}
}
return NULL;
}
/*
* Iterate over the tagged entries, doing a radix_tree_iter_retry() as we find
* things that have been removed and randomly resetting our iteration to the
* next chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *tagged_iteration_fn(void *arg)
{
struct radix_tree_iter iter;
void **slot;
while (!test_complete) {
rcu_read_lock();
radix_tree_for_each_tagged(slot, &tree, &iter, 0, TAG) {
void *entry;
int i;
/* busy wait to let removals happen */
for (i = 0; i < 1000000; i++)
;
entry = radix_tree_deref_slot(slot);
if (unlikely(!entry))
continue;
if (radix_tree_deref_retry(entry)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
if (rand() % 50 == 0)
slot = radix_tree_iter_next(&iter);
}
rcu_read_unlock();
}
return NULL;
}
/*
* Iterate over the entries, doing a radix_tree_iter_retry() as we find things
* that have been removed and randomly resetting our iteration to the next
* chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *untagged_iteration_fn(void *arg)
{
struct radix_tree_iter iter;
void **slot;
while (!test_complete) {
rcu_read_lock();
radix_tree_for_each_slot(slot, &tree, &iter, 0) {
void *entry;
int i;
/* busy wait to let removals happen */
for (i = 0; i < 1000000; i++)
;
entry = radix_tree_deref_slot(slot);
if (unlikely(!entry))
continue;
if (radix_tree_deref_retry(entry)) {
slot = radix_tree_iter_retry(&iter);
continue;
}
if (rand() % 50 == 0)
slot = radix_tree_iter_next(&iter);
}
rcu_read_unlock();
}
return NULL;
}
/*
* Randomly remove entries to help induce radix_tree_iter_retry() calls in the
* two iteration functions.
*/
static void *remove_entries_fn(void *arg)
{
while (!test_complete) {
int pgoff;
pgoff = rand() % 100;
pthread_mutex_lock(&tree_lock);
item_delete(&tree, pgoff);
pthread_mutex_unlock(&tree_lock);
}
return NULL;
}
/* This is a unit test for a bug found by the syzkaller tester */
void iteration_test(void)
{
int i;
printf("Running iteration tests for 10 seconds\n");
srand(time(0));
test_complete = false;
if (pthread_create(&threads[0], NULL, tagged_iteration_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[1], NULL, untagged_iteration_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[2], NULL, add_entries_fn, NULL)) {
perror("pthread_create");
exit(1);
}
if (pthread_create(&threads[3], NULL, remove_entries_fn, NULL)) {
perror("pthread_create");
exit(1);
}
sleep(10);
test_complete = true;
for (i = 0; i < NUM_THREADS; i++) {
if (pthread_join(threads[i], NULL)) {
perror("pthread_join");
exit(1);
}
}
item_kill_tree(&tree);
}
......@@ -332,6 +332,7 @@ int main(int argc, char **argv)
regression1_test();
regression2_test();
regression3_test();
iteration_test();
single_thread_tests(long_run);
sleep(1);
......
......@@ -27,6 +27,7 @@ void item_kill_tree(struct radix_tree_root *root);
void tag_check(void);
void multiorder_checks(void);
void iteration_test(void);
struct item *
item_tag_set(struct radix_tree_root *root, unsigned long index, int tag);
......
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