The kunit_remove_resource() function is used to unlink a resource from
the list of resources in the test, making it no longer show up in
kunit_find_resource().
However, this could lead to a race condition if two threads called
kunit_remove_resource() on the same resource at the same time: the
resource would be removed from the list twice (causing a crash at the
second list_del()), and the refcount for the resource would be
decremented twice (instead of once, for the reference held by the
resource list).
Fix both problems, the first by using list_del_init(), and the second by
checking if the resource has already been removed using list_empty(),
and only decrementing its refcount if it has not.
Also add a KUnit test for the kunit_remove_resource() function which
tests this behaviour.
Reported-by: Daniel Latypov <[email protected]>
Signed-off-by: David Gow <[email protected]>
---
lib/kunit/kunit-test.c | 35 +++++++++++++++++++++++++++++++++++
lib/kunit/test.c | 8 ++++++--
2 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
index 555601d17f79..9005034558aa 100644
--- a/lib/kunit/kunit-test.c
+++ b/lib/kunit/kunit-test.c
@@ -190,6 +190,40 @@ static void kunit_resource_test_destroy_resource(struct kunit *test)
KUNIT_EXPECT_TRUE(test, list_empty(&ctx->test.resources));
}
+static void kunit_resource_test_remove_resource(struct kunit *test)
+{
+ struct kunit_test_resource_context *ctx = test->priv;
+ struct kunit_resource *res = kunit_alloc_and_get_resource(
+ &ctx->test,
+ fake_resource_init,
+ fake_resource_free,
+ GFP_KERNEL,
+ ctx);
+
+ /* The resource is in the list */
+ KUNIT_EXPECT_FALSE(test, list_empty(&ctx->test.resources));
+
+ /* Remove the resource. The pointer is still valid, but it can't be
+ * found.
+ */
+ kunit_remove_resource(test, res);
+ KUNIT_EXPECT_TRUE(test, list_empty(&ctx->test.resources));
+ /* We haven't been freed yet. */
+ KUNIT_EXPECT_TRUE(test, ctx->is_resource_initialized);
+
+ /* Removing the resource multiple times is valid. */
+ kunit_remove_resource(test, res);
+ KUNIT_EXPECT_TRUE(test, list_empty(&ctx->test.resources));
+ /* Despite having been removed twice (from only one reference), the
+ * resource still has not been freed.
+ */
+ KUNIT_EXPECT_TRUE(test, ctx->is_resource_initialized);
+
+ /* Free the resource. */
+ kunit_put_resource(res);
+ KUNIT_EXPECT_FALSE(test, ctx->is_resource_initialized);
+}
+
static void kunit_resource_test_cleanup_resources(struct kunit *test)
{
int i;
@@ -387,6 +421,7 @@ static struct kunit_case kunit_resource_test_cases[] = {
KUNIT_CASE(kunit_resource_test_init_resources),
KUNIT_CASE(kunit_resource_test_alloc_resource),
KUNIT_CASE(kunit_resource_test_destroy_resource),
+ KUNIT_CASE(kunit_resource_test_remove_resource),
KUNIT_CASE(kunit_resource_test_cleanup_resources),
KUNIT_CASE(kunit_resource_test_proper_free_ordering),
KUNIT_CASE(kunit_resource_test_static),
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 3bca3bf5c15b..8411cdfe40a8 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -680,11 +680,15 @@ EXPORT_SYMBOL_GPL(kunit_alloc_and_get_resource);
void kunit_remove_resource(struct kunit *test, struct kunit_resource *res)
{
unsigned long flags;
+ bool was_linked;
spin_lock_irqsave(&test->lock, flags);
- list_del(&res->node);
+ was_linked = !list_empty(&res->node);
+ list_del_init(&res->node);
spin_unlock_irqrestore(&test->lock, flags);
- kunit_put_resource(res);
+
+ if (was_linked)
+ kunit_put_resource(res);
}
EXPORT_SYMBOL_GPL(kunit_remove_resource);
--
2.35.1.894.gb6a874cedc-goog
On Fri, Mar 18, 2022 at 2:50 AM David Gow <[email protected]> wrote:
>
> The kunit_remove_resource() function is used to unlink a resource from
> the list of resources in the test, making it no longer show up in
> kunit_find_resource().
>
> However, this could lead to a race condition if two threads called
> kunit_remove_resource() on the same resource at the same time: the
> resource would be removed from the list twice (causing a crash at the
> second list_del()), and the refcount for the resource would be
> decremented twice (instead of once, for the reference held by the
> resource list).
>
> Fix both problems, the first by using list_del_init(), and the second by
> checking if the resource has already been removed using list_empty(),
> and only decrementing its refcount if it has not.
>
> Also add a KUnit test for the kunit_remove_resource() function which
> tests this behaviour.
>
> Reported-by: Daniel Latypov <[email protected]>
> Signed-off-by: David Gow <[email protected]>
Reviewed-by: Brendan Higgins <[email protected]>