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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Davidlohr Bueso <dave@stgolabs.net>,
        Davidlohr Bueso <dbueso@suse.de>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.9 218/219] locking/locktorture: Fix num
 reader/writer corner cases
Thread-Topic: [PATCH AUTOSEL for 4.9 218/219] locking/locktorture: Fix num
 reader/writer corner cases
Thread-Index: AQHTsz8sRxoEQAjVN0mTV3/6ThEeCA==
Date:   Sat, 3 Mar 2018 22:30:03 +0000
Message-ID: <20180303222716.26640-218-alexander.levin@microsoft.com>
References: <20180303222716.26640-1-alexander.levin@microsoft.com>
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From: Davidlohr Bueso <dave@stgolabs.net>

[ Upstream commit 2ce77d16db4240dd2e422fc0a5c26d3e2ec03446 ]

Things can explode for locktorture if the user does combinations
of nwriters_stress=3D0 nreaders_stress=3D0. Fix this by not assuming
we always want to torture writer threads.

Reported-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 kernel/locking/locktorture.c | 76 +++++++++++++++++++++++++---------------=
----
 1 file changed, 44 insertions(+), 32 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index d3de04b12f8c..babc67cfed69 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -641,8 +641,7 @@ static void __torture_print_stats(char *page,
 {
 	bool fail =3D 0;
 	int i, n_stress;
-	long max =3D 0;
-	long min =3D statp[0].n_lock_acquired;
+	long max =3D 0, min =3D statp ? statp[0].n_lock_acquired : 0;
 	long long sum =3D 0;
=20
 	n_stress =3D write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
@@ -749,7 +748,7 @@ static void lock_torture_cleanup(void)
 	 * such, only perform the underlying torture-specific cleanups,
 	 * and avoid anything related to locktorture.
 	 */
-	if (!cxt.lwsa)
+	if (!cxt.lwsa && !cxt.lrsa)
 		goto end;
=20
 	if (writer_tasks) {
@@ -823,6 +822,13 @@ static int __init lock_torture_init(void)
 		firsterr =3D -EINVAL;
 		goto unwind;
 	}
+
+	if (nwriters_stress =3D=3D 0 && nreaders_stress =3D=3D 0) {
+		pr_alert("lock-torture: must run at least one locking thread\n");
+		firsterr =3D -EINVAL;
+		goto unwind;
+	}
+
 	if (cxt.cur_ops->init)
 		cxt.cur_ops->init();
=20
@@ -846,17 +852,19 @@ static int __init lock_torture_init(void)
 #endif
=20
 	/* Initialize the statistics so that each run gets its own numbers. */
+	if (nwriters_stress) {
+		lock_is_write_held =3D 0;
+		cxt.lwsa =3D kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KE=
RNEL);
+		if (cxt.lwsa =3D=3D NULL) {
+			VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
+			firsterr =3D -ENOMEM;
+			goto unwind;
+		}
=20
-	lock_is_write_held =3D 0;
-	cxt.lwsa =3D kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KER=
NEL);
-	if (cxt.lwsa =3D=3D NULL) {
-		VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
-		firsterr =3D -ENOMEM;
-		goto unwind;
-	}
-	for (i =3D 0; i < cxt.nrealwriters_stress; i++) {
-		cxt.lwsa[i].n_lock_fail =3D 0;
-		cxt.lwsa[i].n_lock_acquired =3D 0;
+		for (i =3D 0; i < cxt.nrealwriters_stress; i++) {
+			cxt.lwsa[i].n_lock_fail =3D 0;
+			cxt.lwsa[i].n_lock_acquired =3D 0;
+		}
 	}
=20
 	if (cxt.cur_ops->readlock) {
@@ -873,19 +881,21 @@ static int __init lock_torture_init(void)
 			cxt.nrealreaders_stress =3D cxt.nrealwriters_stress;
 		}
=20
-		lock_is_read_held =3D 0;
-		cxt.lrsa =3D kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KE=
RNEL);
-		if (cxt.lrsa =3D=3D NULL) {
-			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
-			firsterr =3D -ENOMEM;
-			kfree(cxt.lwsa);
-			cxt.lwsa =3D NULL;
-			goto unwind;
-		}
-
-		for (i =3D 0; i < cxt.nrealreaders_stress; i++) {
-			cxt.lrsa[i].n_lock_fail =3D 0;
-			cxt.lrsa[i].n_lock_acquired =3D 0;
+		if (nreaders_stress) {
+			lock_is_read_held =3D 0;
+			cxt.lrsa =3D kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_K=
ERNEL);
+			if (cxt.lrsa =3D=3D NULL) {
+				VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
+				firsterr =3D -ENOMEM;
+				kfree(cxt.lwsa);
+				cxt.lwsa =3D NULL;
+				goto unwind;
+			}
+
+			for (i =3D 0; i < cxt.nrealreaders_stress; i++) {
+				cxt.lrsa[i].n_lock_fail =3D 0;
+				cxt.lrsa[i].n_lock_acquired =3D 0;
+			}
 		}
 	}
=20
@@ -915,12 +925,14 @@ static int __init lock_torture_init(void)
 			goto unwind;
 	}
=20
-	writer_tasks =3D kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]=
),
-			       GFP_KERNEL);
-	if (writer_tasks =3D=3D NULL) {
-		VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
-		firsterr =3D -ENOMEM;
-		goto unwind;
+	if (nwriters_stress) {
+		writer_tasks =3D kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0=
]),
+				       GFP_KERNEL);
+		if (writer_tasks =3D=3D NULL) {
+			VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
+			firsterr =3D -ENOMEM;
+			goto unwind;
+		}
 	}
=20
 	if (cxt.cur_ops->readlock) {
--=20
2.14.1