[PATCH v3 16/30] locking/lockdep: Use lock type enum to explicitly specify read or write locks

Yuyang Du
2019-06-28T09:16:58Z

Add an enum to formally quantify lock types. No functional change.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
include/linux/lockdep.h | 27 ++++++++++++++++++++-------
include/linux/rcupdate.h | 2 +-
kernel/locking/lockdep.c | 19 +++++++++++--------
3 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 981718b..eb26e93 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -353,10 +353,18 @@ static inline int lockdep_match_key(struct lockdep_map *lock,
*
* Values for "read":
*
- * 0: exclusive (write) acquire
- * 1: read-acquire (no recursion allowed)
- * 2: read-acquire with same-instance recursion allowed
- *
+ * LOCK_TYPE_EXCLUSIVE (LOCK_TYPE_WRITE): exclusive (write) acquire
+ * LOCK_TYPE_READ: read-acquire (no recursion allowed)
+ * LOCK_TYPE_RECURSIVE: read-acquire with same-instance recursion allowed
+ */
+enum lock_type {
+ LOCK_TYPE_EXCLUSIVE = 0,
+ LOCK_TYPE_WRITE = 0,
+ LOCK_TYPE_READ,
+ LOCK_TYPE_RECURSIVE,
+};
+
+/*
* Values for check:
*
* 0: simple checks (freeing, held-at-exit-time, etc.)
@@ -602,9 +610,14 @@ static inline void print_irqtrace_events(struct task_struct *curr)
* on the per lock-class debug mode:
*/

-#define lock_acquire_exclusive(l, s, t, n, i) lock_acquire(l, s, t, 0, 1, n, i)
-#define lock_acquire_shared(l, s, t, n, i) lock_acquire(l, s, t, 1, 1, n, i)
-#define lock_acquire_shared_recursive(l, s, t, n, i) lock_acquire(l, s, t, 2, 1, n, i)
+#define lock_acquire_exclusive(l, s, t, n, i) \
+ lock_acquire(l, s, t, LOCK_TYPE_EXCLUSIVE, 1, n, i)
+
+#define lock_acquire_shared(l, s, t, n, i) \
+ lock_acquire(l, s, t, LOCK_TYPE_READ, 1, n, i)
+
+#define lock_acquire_shared_recursive(l, s, t, n, i) \
+ lock_acquire(l, s, t, LOCK_TYPE_RECURSIVE, 1, n, i)

#define spin_acquire(l, s, t, i) lock_acquire_exclusive(l, s, t, NULL, i)
#define spin_acquire_nest(l, s, t, n, i) lock_acquire_exclusive(l, s, t, n, i)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b25d208..d0279da 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -205,7 +205,7 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }

static inline void rcu_lock_acquire(struct lockdep_map *map)
{
- lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
+ lock_acquire(map, 0, 0, LOCK_TYPE_RECURSIVE, 0, NULL, _THIS_IP_);
}

static inline void rcu_lock_release(struct lockdep_map *map)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3b655fd..3c97d71 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2356,7 +2356,10 @@ static inline void inc_chains(void)
* (Note that this has to be done separately, because the graph cannot
* detect such classes of deadlocks.)
*
- * Returns: 0 on deadlock detected, 1 on OK, 2 on recursive read
+ * Returns:
+ * 0: on deadlock detected;
+ * 1: on OK;
+ * LOCK_TYPE_RECURSIVE: on recursive read
*/
static int
check_deadlock_current(struct task_struct *curr, struct held_lock *next)
@@ -2378,15 +2381,15 @@ static inline void inc_chains(void)
* Allow read-after-read recursion of the same
* lock class (i.e. read_lock(lock)+read_lock(lock)):
*/
- if ((next->read == 2) && prev->read)
- return 2;
+ if ((next->read == LOCK_TYPE_RECURSIVE) && prev->read)
+ return LOCK_TYPE_RECURSIVE;

/*
* We're holding the nest_lock, which serializes this lock's
* nesting behaviour.
*/
if (nest)
- return 2;
+ return LOCK_TYPE_RECURSIVE;

print_deadlock_bug(curr, prev, next);
return 0;
@@ -2489,7 +2492,7 @@ static inline void inc_chains(void)
* write-lock never takes any other locks, then the reads are
* equivalent to a NOP.
*/
- if (next->read == 2 || prev->read == 2)
+ if (next->read == LOCK_TYPE_RECURSIVE || prev->read == LOCK_TYPE_RECURSIVE)
return 1;

if (!trace->nr_entries && !save_trace(trace))
@@ -2869,7 +2872,7 @@ static int validate_chain(struct task_struct *curr, struct held_lock *next,
* chain, and if it's not a second recursive-read lock. If
* not, there is no need to check further.
*/
- if (!(chain->depth > 1 && ret != 2))
+ if (!(chain->depth > 1 && ret != LOCK_TYPE_RECURSIVE))
goto out_unlock;
}

@@ -2878,7 +2881,7 @@ static int validate_chain(struct task_struct *curr, struct held_lock *next,
* added:
*/
if (chain) {
- if (hlock->read != 2 && hlock->check) {
+ if (hlock->read != LOCK_TYPE_RECURSIVE && hlock->check) {
int distance = curr->lockdep_depth - depth + 1;

if (!check_prev_add(curr, hlock, next, distance,
@@ -4132,7 +4135,7 @@ static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip)
curr->curr_chain_key = hlock->prev_chain_key;

WARN(hlock->read, "downgrading a read lock");
- hlock->read = 1;
+ hlock->read = LOCK_TYPE_READ;
hlock->acquire_ip = ip;

if (reacquire_held_locks(curr, depth, i, &merged))
--
1.8.3.1