[RFC PATCH 07/12] locking/lockdep: Add support for nested terminal locks

Waiman Long
2018-11-08T20:35:55Z

There are use cases where we want to allow 2-level nesting of one
terminal lock underneath another one. So the terminal lock type is now
extended to support a new nested terminal lock where it can allow the
acquisition of another regular terminal lock underneath it.

Signed-off-by: Waiman Long <longman@redhat.com>
---
include/linux/lockdep.h | 9 ++++++++-
kernel/locking/lockdep.c | 15 +++++++++++++--
kernel/locking/lockdep_internals.h | 2 +-
3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c5ff8c5..ed4d177 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -147,12 +147,16 @@ struct lock_class_stats {
* 1) LOCKDEP_FLAG_NOVALIDATE: No full validation, just simple checks.
* 2) LOCKDEP_FLAG_TERMINAL: This is a terminal lock where lock/unlock on
* another lock within its critical section is not allowed.
+ * 3) LOCKDEP_FLAG_TERMINAL_NESTED: This is a terminal lock that allows
+ * one more regular terminal lock to be nested underneath it.
*/
#define LOCKDEP_FLAG_NOVALIDATE (1 << 0)
#define LOCKDEP_FLAG_TERMINAL (1 << 1)
+#define LOCKDEP_FLAG_TERMINAL_NESTED (1 << 2)

#define LOCKDEP_NOCHECK_FLAGS (LOCKDEP_FLAG_NOVALIDATE |\
- LOCKDEP_FLAG_TERMINAL)
+ LOCKDEP_FLAG_TERMINAL |\
+ LOCKDEP_FLAG_TERMINAL_NESTED)

/*
* Map the lock object (the lock instance) to the lock-class object.
@@ -314,6 +318,8 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
do { (lock)->dep_map.flags |= LOCKDEP_FLAG_NOVALIDATE; } while (0)
#define lockdep_set_terminal_class(lock) \
do { (lock)->dep_map.flags |= LOCKDEP_FLAG_TERMINAL; } while (0)
+#define lockdep_set_terminal_nested_class(lock) \
+ do { (lock)->dep_map.flags |= LOCKDEP_FLAG_TERMINAL_NESTED; } while (0)

/*
* Compare locking classes
@@ -431,6 +437,7 @@ static inline void lockdep_on(void)

#define lockdep_set_novalidate_class(lock) do { } while (0)
#define lockdep_set_terminal_class(lock) do { } while (0)
+#define lockdep_set_terminal_nested_class(lock) do { } while (0)

/*
* We don't define lockdep_match_class() and lockdep_match_key() for !LOCKDEP
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 02631a0..2b75613 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3268,13 +3268,24 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
class_idx = class - lock_classes + 1;

if (depth) {
+ int prev_type;
+
hlock = curr->held_locks + depth - 1;

/*
- * Warn if the previous lock is a terminal lock.
+ * Warn if the previous lock is a terminal lock or the
+ * previous lock is a nested terminal lock and the current
+ * one isn't a regular terminal lock.
*/
- if (DEBUG_LOCKS_WARN_ON(hlock_is_terminal(hlock)))
+ prev_type = hlock_is_terminal(hlock);
+ if (DEBUG_LOCKS_WARN_ON((prev_type == LOCKDEP_FLAG_TERMINAL) ||
+ ((prev_type == LOCKDEP_FLAG_TERMINAL_NESTED) &&
+ (flags_is_terminal(class->flags) !=
+ LOCKDEP_FLAG_TERMINAL)))) {
+ pr_warn("Terminal lock error: prev lock = %s, curr lock = %s\n",
+ hlock->instance->name, class->name);
return 0;
+ }

if (hlock->class_idx == class_idx && nest_lock) {
if (hlock->references) {
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 271fba8..abe646a 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -215,5 +215,5 @@ static inline unsigned long debug_class_ops_read(struct lock_class *class)

static inline unsigned int flags_is_terminal(unsigned int flags)
{
- return flags & LOCKDEP_FLAG_TERMINAL;
+ return flags & (LOCKDEP_FLAG_TERMINAL|LOCKDEP_FLAG_TERMINAL_NESTED);
}
--
1.8.3.1