linux-kernel - [tip: locking/core] locking/locktorture: Fix false positive circular locking splat in ww

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Date:   Fri, 19 Mar 2021 12:54:17 -0000
From:   "tip-bot2 for Waiman Long" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/locktorture: Fix false positive circular
 locking splat in ww_mutex test

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     2ea55bbba23e9d36996299664d618393c8602646
Gitweb:        https://git.kernel.org/tip/2ea55bbba23e9d36996299664d618393c8602646
Author:        Waiman Long <longman@...hat.com>
AuthorDate:    Thu, 18 Mar 2021 13:28:11 -04:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 19 Mar 2021 12:13:09 +01:00

locking/locktorture: Fix false positive circular locking splat in ww_mutex test

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@...radead.org>
Signed-off-by: Waiman Long <longman@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20210318172814.4400-3-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 0ab94e1..3c27f43 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,