linux-kernel - [RFC v7 18/19] locking/selftest: Add test cases for queued_read

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Message-Id: <20200807074238.1632519-19-boqun.feng@gmail.com>
Date:   Fri,  7 Aug 2020 15:42:37 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC v7 18/19] locking/selftest: Add test cases for queued_read_lock()

Add two self test cases for the following case:

	P0:			P1:			P2:

				<in irq handler>
	spin_lock_irq(&slock)	read_lock(&rwlock)
							write_lock_irq(&rwlock)
	read_lock(&rwlock)	spin_lock(&slock)

, which is a deadlock, as the read_lock() on P0 cannot get the lock
because of the fairness.

	P0:			P1:			P2:

	<in irq handler>
	spin_lock(&slock)	read_lock(&rwlock)
							write_lock(&rwlock)
	read_lock(&rwlock)	spin_lock_irq(&slock)

, which is not a deadlock, as the read_lock() on P0 can get the lock
because it could use the unfair fastpass.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 lib/locking-selftest.c | 104 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 4264cf4b60bb..17f8f6f37165 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -2201,6 +2201,108 @@ static void ww_tests(void)
 	pr_cont("\n");
 }
 
+
+/*
+ * <in hardirq handler>
+ * read_lock(&A);
+ *			<hardirq disable>
+ *			spin_lock(&B);
+ * spin_lock(&B);
+ *			read_lock(&A);
+ *
+ * is a deadlock.
+ */
+static void queued_read_lock_hardirq_RE_Er(void)
+{
+	HARDIRQ_ENTER();
+	read_lock(&rwlock_A);
+	LOCK(B);
+	UNLOCK(B);
+	read_unlock(&rwlock_A);
+	HARDIRQ_EXIT();
+
+	HARDIRQ_DISABLE();
+	LOCK(B);
+	read_lock(&rwlock_A);
+	read_unlock(&rwlock_A);
+	UNLOCK(B);
+	HARDIRQ_ENABLE();
+}
+
+/*
+ * <in hardirq handler>
+ * spin_lock(&B);
+ *			<hardirq disable>
+ *			read_lock(&A);
+ * read_lock(&A);
+ *			spin_lock(&B);
+ *
+ * is not a deadlock.
+ */
+static void queued_read_lock_hardirq_ER_rE(void)
+{
+	HARDIRQ_ENTER();
+	LOCK(B);
+	read_lock(&rwlock_A);
+	read_unlock(&rwlock_A);
+	UNLOCK(B);
+	HARDIRQ_EXIT();
+
+	HARDIRQ_DISABLE();
+	read_lock(&rwlock_A);
+	LOCK(B);
+	UNLOCK(B);
+	read_unlock(&rwlock_A);
+	HARDIRQ_ENABLE();
+}
+
+/*
+ * <hardirq disable>
+ * spin_lock(&B);
+ *			read_lock(&A);
+ *			<in hardirq handler>
+ *			spin_lock(&B);
+ * read_lock(&A);
+ *
+ * is a deadlock. Because the two read_lock()s are both non-recursive readers.
+ */
+static void queued_read_lock_hardirq_inversion(void)
+{
+
+	HARDIRQ_ENTER();
+	LOCK(B);
+	UNLOCK(B);
+	HARDIRQ_EXIT();
+
+	HARDIRQ_DISABLE();
+	LOCK(B);
+	read_lock(&rwlock_A);
+	read_unlock(&rwlock_A);
+	UNLOCK(B);
+	HARDIRQ_ENABLE();
+
+	read_lock(&rwlock_A);
+	read_unlock(&rwlock_A);
+}
+
+static void queued_read_lock_tests(void)
+{
+	printk("  --------------------------------------------------------------------------\n");
+	printk("  | queued read lock tests |\n");
+	printk("  ---------------------------\n");
+	print_testname("hardirq read-lock/lock-read");
+	dotest(queued_read_lock_hardirq_RE_Er, FAILURE, LOCKTYPE_RWLOCK);
+	pr_cont("\n");
+
+	print_testname("hardirq lock-read/read-lock");
+	dotest(queued_read_lock_hardirq_ER_rE, SUCCESS, LOCKTYPE_RWLOCK);
+	pr_cont("\n");
+
+	print_testname("hardirq inversion");
+	dotest(queued_read_lock_hardirq_inversion, FAILURE, LOCKTYPE_RWLOCK);
+	pr_cont("\n");
+}
+
 void locking_selftest(void)
 {
 	/*
@@ -2318,6 +2420,8 @@ void locking_selftest(void)
 	/*
 	 * queued_read_lock() specific test cases can be put here
 	 */
+	if (IS_ENABLED(CONFIG_QUEUED_RWLOCKS))
+		queued_read_lock_tests();
 
 	if (unexpected_testcase_failures) {
 		printk("-----------------------------------------------------------------\n");
-- 
2.28.0