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

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index caadc4dd33685c1d031f8438d13d932e3fcb8394..002d1ec098521e9c564defe2462398d25cb74a4e 100644 (file)
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -396,6 +396,49 @@ static void rwsem_ABBA1(void)
        MU(Y1); // should fail
 }
 
+/*
+ * 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)
@@ -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");
 
        /*