linux-kernel - [PATCH-tip 5/5] locking/locktorture: locking/locktorture: Fix incorrect use of ww_acquire_ctx in ww

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Date:   Thu, 18 Mar 2021 13:28:14 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>
Cc:     linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH-tip 5/5] locking/locktorture: locking/locktorture: Fix incorrect use of ww_acquire_ctx in ww_mutex test

The ww_acquire_ctx structure for ww_mutex needs to persist for a complete
lock/unlock cycle. In the ww_mutex test in locktorture, however, both
ww_acquire_init() and ww_acquire_fini() are called within the lock
function only. This causes a lockdep splat of "WARNING: Nested lock
was not taken" when lockdep is enabled in the kernel.

To fix this problem, we need to move the ww_acquire_fini() after
the ww_mutex_unlock() in torture_ww_mutex_unlock(). This is done by
allocating a global array of ww_acquire_ctx structures. Each locking
thread is associated with its own ww_acquire_ctx via the unique thread
id it has so that both the lock and unlock functions can access the
same ww_acquire_ctx structure.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/locking/locktorture.c | 39 +++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 90a975a95a13..b3adb40549bf 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -374,15 +374,27 @@ static struct lock_torture_ops mutex_lock_ops = {
  */
 static DEFINE_WD_CLASS(torture_ww_class);
 static struct ww_mutex torture_ww_mutex_0, torture_ww_mutex_1, torture_ww_mutex_2;
+static struct ww_acquire_ctx *ww_acquire_ctxs;
 
 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);
+
+	ww_acquire_ctxs = kmalloc_array(cxt.nrealwriters_stress,
+					sizeof(*ww_acquire_ctxs),
+					GFP_KERNEL);
+	if (!ww_acquire_ctxs)
+		VERBOSE_TOROUT_STRING("ww_acquire_ctx: Out of memory");
+}
+
+static void torture_ww_mutex_exit(void)
+{
+	kfree(ww_acquire_ctxs);
 }
 
-static int torture_ww_mutex_lock(int tid __maybe_unused)
+static int torture_ww_mutex_lock(int tid)
 __acquires(torture_ww_mutex_0)
 __acquires(torture_ww_mutex_1)
 __acquires(torture_ww_mutex_2)
@@ -392,7 +404,7 @@ __acquires(torture_ww_mutex_2)
 		struct list_head link;
 		struct ww_mutex *lock;
 	} locks[3], *ll, *ln;
-	struct ww_acquire_ctx ctx;
+	struct ww_acquire_ctx *ctx = &ww_acquire_ctxs[tid];
 
 	locks[0].lock = &torture_ww_mutex_0;
 	list_add(&locks[0].link, &list);
@@ -403,12 +415,12 @@ __acquires(torture_ww_mutex_2)
 	locks[2].lock = &torture_ww_mutex_2;
 	list_add(&locks[2].link, &list);
 
-	ww_acquire_init(&ctx, &torture_ww_class);
+	ww_acquire_init(ctx, &torture_ww_class);
 
 	list_for_each_entry(ll, &list, link) {
 		int err;
 
-		err = ww_mutex_lock(ll->lock, &ctx);
+		err = ww_mutex_lock(ll->lock, ctx);
 		if (!err)
 			continue;
 
@@ -419,26 +431,29 @@ __acquires(torture_ww_mutex_2)
 		if (err != -EDEADLK)
 			return err;
 
-		ww_mutex_lock_slow(ll->lock, &ctx);
+		ww_mutex_lock_slow(ll->lock, ctx);
 		list_move(&ll->link, &list);
 	}
 
-	ww_acquire_fini(&ctx);
 	return 0;
 }
 
-static void torture_ww_mutex_unlock(int tid __maybe_unused)
+static void torture_ww_mutex_unlock(int tid)
 __releases(torture_ww_mutex_0)
 __releases(torture_ww_mutex_1)
 __releases(torture_ww_mutex_2)
 {
+	struct ww_acquire_ctx *ctx = &ww_acquire_ctxs[tid];
+
 	ww_mutex_unlock(&torture_ww_mutex_0);
 	ww_mutex_unlock(&torture_ww_mutex_1);
 	ww_mutex_unlock(&torture_ww_mutex_2);
+	ww_acquire_fini(ctx);
 }
 
 static struct lock_torture_ops ww_mutex_lock_ops = {
 	.init		= torture_ww_mutex_init,
+	.exit		= torture_ww_mutex_exit,
 	.writelock	= torture_ww_mutex_lock,
 	.write_delay	= torture_mutex_delay,
 	.task_boost     = torture_boost_dummy,
@@ -924,16 +939,16 @@ static int __init lock_torture_init(void)
 		goto unwind;
 	}
 
-	if (cxt.cur_ops->init) {
-		cxt.cur_ops->init();
-		cxt.init_called = true;
-	}
-
 	if (nwriters_stress >= 0)
 		cxt.nrealwriters_stress = nwriters_stress;
 	else
 		cxt.nrealwriters_stress = 2 * num_online_cpus();
 
+	if (cxt.cur_ops->init) {
+		cxt.cur_ops->init();
+		cxt.init_called = true;
+	}
+
 #ifdef CONFIG_DEBUG_MUTEXES
 	if (str_has_prefix(torture_type, "mutex"))
 		cxt.debug_lock = true;
-- 
2.18.1