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Date:   Thu, 27 Aug 2020 07:54:17 -0000
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Subject: [tip: locking/core] lockdep/selftest: Add a R-L/L-W test case
 specific to chain cache behavior
Cc:     Boqun Feng <boqun.feng@gmail.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
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The following commit has been merged into the locking/core branch of tip:

Commit-ID:     d4f200e579e96051f1f081f795820787826eb234
Gitweb:        https://git.kernel.org/tip/d4f200e579e96051f1f081f795820787826eb234
Author:        Boqun Feng <boqun.feng@gmail.com>
AuthorDate:    Fri, 07 Aug 2020 15:42:32 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 26 Aug 2020 12:42:06 +02:00

lockdep/selftest: Add a R-L/L-W test case specific to chain cache behavior

As our chain cache doesn't differ read/write locks, so even we can
detect a read-lock/lock-write deadlock in check_noncircular(), we can
still be fooled if a read-lock/lock-read case(which is not a deadlock)
comes first.

So introduce this test case to test specific to the chain cache behavior
on detecting recursive read lock related deadlocks.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-14-boqun.feng@gmail.com
---
 lib/locking-selftest.c | 47 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index caadc4d..002d1ec 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -400,6 +400,49 @@ static void rwsem_ABBA1(void)
  * read_lock(A)
  * spin_lock(B)
  *		spin_lock(B)
+ *		write_lock(A)
+ *
+ * This test case is aimed at poking whether the chain cache prevents us from
+ * detecting a read-lock/lock-write deadlock: if the chain cache doesn't differ
+ * read/write locks, the following case may happen
+ *
+ * 	{ read_lock(A)->lock(B) dependency exists }
+ *
+ * 	P0:
+ * 	lock(B);
+ * 	read_lock(A);
+ *
+ *	{ Not a deadlock, B -> A is added in the chain cache }
+ *
+ *	P1:
+ *	lock(B);
+ *	write_lock(A);
+ *
+ *	{ B->A found in chain cache, not reported as a deadlock }
+ *
+ */
+static void rlock_chaincache_ABBA1(void)
+{
+	RL(X1);
+	L(Y1);
+	U(Y1);
+	RU(X1);
+
+	L(Y1);
+	RL(X1);
+	RU(X1);
+	U(Y1);
+
+	L(Y1);
+	WL(X1);
+	WU(X1);
+	U(Y1); // should fail
+}
+
+/*
+ * read_lock(A)
+ * spin_lock(B)
+ *		spin_lock(B)
  *		read_lock(A)
  */
 static void rlock_ABBA2(void)
@@ -2062,6 +2105,10 @@ void locking_selftest(void)
 	pr_cont("             |");
 	dotest(rwsem_ABBA3, FAILURE, LOCKTYPE_RWSEM);
 
+	print_testname("chain cached mixed R-L/L-W ABBA");
+	pr_cont("             |");
+	dotest(rlock_chaincache_ABBA1, FAILURE, LOCKTYPE_RWLOCK);
+
 	printk("  --------------------------------------------------------------------------\n");
 
 	/*