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Date:   Wed, 23 Jun 2021 08:19:09 -0000
From:   "tip-bot2 for Boqun Feng" <tip-bot2@linutronix.de>
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To:     linux-tip-commits@vger.kernel.org
Subject: [tip: locking/core] locking/selftests: Add a selftest for check_irq_usage()
Cc:     Boqun Feng <boqun.feng@gmail.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org
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The following commit has been merged into the locking/core branch of tip:

Commit-ID:     8946ccc25ed22d957ca7f0b6fac1dcf6d25eaf1f
Gitweb:        https://git.kernel.org/tip/8946ccc25ed22d957ca7f0b6fac1dcf6d25eaf1f
Author:        Boqun Feng <boqun.feng@gmail.com>
AuthorDate:    Sat, 19 Jun 2021 01:01:10 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 22 Jun 2021 16:42:07 +02:00

locking/selftests: Add a selftest for check_irq_usage()

Johannes Berg reported a lockdep problem which could be reproduced by
the special test case introduced in this patch, so add it.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210618170110.3699115-5-boqun.feng@gmail.com
---
 lib/locking-selftest.c | 65 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 65 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index 2d85aba..5c50b09 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -53,6 +53,7 @@ __setup("debug_locks_verbose=", setup_debug_locks_verbose);
 #define LOCKTYPE_WW	0x10
 #define LOCKTYPE_RTMUTEX 0x20
 #define LOCKTYPE_LL	0x40
+#define LOCKTYPE_SPECIAL 0x80
 
 static struct ww_acquire_ctx t, t2;
 static struct ww_mutex o, o2, o3;
@@ -2744,6 +2745,66 @@ static void local_lock_tests(void)
 	pr_cont("\n");
 }
 
+static void hardirq_deadlock_softirq_not_deadlock(void)
+{
+	/* mutex_A is hardirq-unsafe and softirq-unsafe */
+	/* mutex_A -> lock_C */
+	mutex_lock(&mutex_A);
+	HARDIRQ_DISABLE();
+	spin_lock(&lock_C);
+	spin_unlock(&lock_C);
+	HARDIRQ_ENABLE();
+	mutex_unlock(&mutex_A);
+
+	/* lock_A is hardirq-safe */
+	HARDIRQ_ENTER();
+	spin_lock(&lock_A);
+	spin_unlock(&lock_A);
+	HARDIRQ_EXIT();
+
+	/* lock_A -> lock_B */
+	HARDIRQ_DISABLE();
+	spin_lock(&lock_A);
+	spin_lock(&lock_B);
+	spin_unlock(&lock_B);
+	spin_unlock(&lock_A);
+	HARDIRQ_ENABLE();
+
+	/* lock_B -> lock_C */
+	HARDIRQ_DISABLE();
+	spin_lock(&lock_B);
+	spin_lock(&lock_C);
+	spin_unlock(&lock_C);
+	spin_unlock(&lock_B);
+	HARDIRQ_ENABLE();
+
+	/* lock_D is softirq-safe */
+	SOFTIRQ_ENTER();
+	spin_lock(&lock_D);
+	spin_unlock(&lock_D);
+	SOFTIRQ_EXIT();
+
+	/* And lock_D is hardirq-unsafe */
+	SOFTIRQ_DISABLE();
+	spin_lock(&lock_D);
+	spin_unlock(&lock_D);
+	SOFTIRQ_ENABLE();
+
+	/*
+	 * mutex_A -> lock_C -> lock_D is softirq-unsafe -> softirq-safe, not
+	 * deadlock.
+	 *
+	 * lock_A -> lock_B -> lock_C -> lock_D is hardirq-safe ->
+	 * hardirq-unsafe, deadlock.
+	 */
+	HARDIRQ_DISABLE();
+	spin_lock(&lock_C);
+	spin_lock(&lock_D);
+	spin_unlock(&lock_D);
+	spin_unlock(&lock_C);
+	HARDIRQ_ENABLE();
+}
+
 void locking_selftest(void)
 {
 	/*
@@ -2872,6 +2933,10 @@ void locking_selftest(void)
 
 	local_lock_tests();
 
+	print_testname("hardirq_unsafe_softirq_safe");
+	dotest(hardirq_deadlock_softirq_not_deadlock, FAILURE, LOCKTYPE_SPECIAL);
+	pr_cont("\n");
+
 	if (unexpected_testcase_failures) {
 		printk("-----------------------------------------------------------------\n");
 		debug_locks = 0;