From eec4852543e4e6edbb6cab512fd1edc70c1f7a18 Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Tue, 11 Oct 2016 13:51:21 -0700 Subject: [PATCH] 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 3cb9185c6730 ("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.com Signed-off-by: Ross Zwisler Cc: Konstantin Khlebnikov Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Shuah Khan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- tools/testing/radix-tree/Makefile | 3 +- tools/testing/radix-tree/iteration_check.c | 180 +++++++++++++++++++++ tools/testing/radix-tree/main.c | 1 + tools/testing/radix-tree/test.h | 1 + 4 files changed, 184 insertions(+), 1 deletion(-) create mode 100644 tools/testing/radix-tree/iteration_check.c diff --git a/tools/testing/radix-tree/Makefile b/tools/testing/radix-tree/Makefile index 9d0919ed52a4..f2e07f2fd4b4 100644 --- a/tools/testing/radix-tree/Makefile +++ b/tools/testing/radix-tree/Makefile @@ -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) diff --git a/tools/testing/radix-tree/iteration_check.c b/tools/testing/radix-tree/iteration_check.c new file mode 100644 index 000000000000..9adb8e7415a6 --- /dev/null +++ b/tools/testing/radix-tree/iteration_check.c @@ -0,0 +1,180 @@ +/* + * iteration_check.c: test races having to do with radix tree iteration + * Copyright (c) 2016 Intel Corporation + * Author: Ross Zwisler + * + * 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 +#include +#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); +} diff --git a/tools/testing/radix-tree/main.c b/tools/testing/radix-tree/main.c index b7619ff3b552..daa9010693e8 100644 --- a/tools/testing/radix-tree/main.c +++ b/tools/testing/radix-tree/main.c @@ -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); diff --git a/tools/testing/radix-tree/test.h b/tools/testing/radix-tree/test.h index e85131369723..217fb2403f09 100644 --- a/tools/testing/radix-tree/test.h +++ b/tools/testing/radix-tree/test.h @@ -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); -- 2.30.2