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Subject[PATCH v2 2/3] radix-tree tests: add iteration test
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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;

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
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 3b53046..6079ec1 100644
--- a/tools/testing/radix-tree/Makefile
+++ b/tools/testing/radix-tree/Makefile
@@ -3,7 +3,8 @@ CFLAGS += -I. -g -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 0000000..9adb8e7
--- /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 <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);
+}
diff --git a/tools/testing/radix-tree/main.c b/tools/testing/radix-tree/main.c
index b7619ff..daa9010 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 e851313..217fb24 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);
--
2.9.0
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