kunit: Make kunit_remove_resource() idempotent

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 <dlatypov@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
index 8e2fe083a54956b7fedad7aef8a84e03171c1b3e..13d0bd8b07a98fd5973ecbe34902a03bf8443945 100644 (file)
--- 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/resource.c b/lib/kunit/resource.c
index 8f8057aad78fdee1f0d5c70ad6acf183a7860e7a..b3ba0d98d89e3ac7ff950a668dbfeb14eea17cf0 100644 (file)
--- a/lib/kunit/resource.c
+++ b/lib/kunit/resource.c
@@ -98,11 +98,15 @@ 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);