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From:   Waiman Long <longman@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>
Cc:     linux-kernel@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>,
        Waiman Long <longman@redhat.com>
Subject: [PATCH-tip 2/5] locking/locktorture: Fix false positive circular locking splat in ww_mutex test
Date:   Thu, 18 Mar 2021 13:28:11 -0400
Message-Id: <20210318172814.4400-3-longman@redhat.com>
In-Reply-To: <20210318172814.4400-1-longman@redhat.com>
References: <20210318172814.4400-1-longman@redhat.com>
Precedence: bulk

In order to avoid false positive circular locking lockdep splat
when runnng the ww_mutex torture test, we need to make sure that
the ww_mutexes have the same lock class as the acquire_ctx. This
means the ww_mutexes must have the same lockdep key as the
acquire_ctx. Unfortunately the current DEFINE_WW_MUTEX() macro fails
to do that. As a result, we add an init method for the ww_mutex test
to do explicit ww_mutex_init()'s of the ww_mutexes to avoid the false
positive warning.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/locktorture.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 0ab94e1f1276..3c27f43ab3e8 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -357,10 +357,20 @@ static struct lock_torture_ops mutex_lock_ops = {
 };
 
 #include <linux/ww_mutex.h>
+/*
+ * The torture ww_mutexes should belong to the same lock class as
+ * torture_ww_class to avoid lockdep problem. The ww_mutex_init()
+ * function is called for initialization to ensure that.
+ */
 static DEFINE_WD_CLASS(torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_0, &torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_1, &torture_ww_class);
-static DEFINE_WW_MUTEX(torture_ww_mutex_2, &torture_ww_class);
+static struct ww_mutex torture_ww_mutex_0, torture_ww_mutex_1, torture_ww_mutex_2;
+
+static void torture_ww_mutex_init(void)
+{
+	ww_mutex_init(&torture_ww_mutex_0, &torture_ww_class);
+	ww_mutex_init(&torture_ww_mutex_1, &torture_ww_class);
+	ww_mutex_init(&torture_ww_mutex_2, &torture_ww_class);
+}
 
 static int torture_ww_mutex_lock(void)
 __acquires(torture_ww_mutex_0)
@@ -418,6 +428,7 @@ __releases(torture_ww_mutex_2)
 }
 
 static struct lock_torture_ops ww_mutex_lock_ops = {
+	.init		= torture_ww_mutex_init,
 	.writelock	= torture_ww_mutex_lock,
 	.write_delay	= torture_mutex_delay,
 	.task_boost     = torture_boost_dummy,
-- 
2.18.1