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Subject[tip: locking/core] locking/selftests: Add a selftest for check_irq_usage()
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;
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