[PATCH v2 02/17] locking/lockdep: Add read-write type for dependency

Yuyang Du
2019-05-16T08:00:34Z

Direct dependency needs to keep track of its locks' read-write types. A
union field is added to lock_list struct so the type is stored there as
this:

lock_type[1] (u16), lock_type[0] (u16)

or:

dep_type (int)

where value:

0: exclusive / write
1: read
2: recursive read

Note that (int) dep_type value may vary with different architectural
endianness, so use helper functions to operate on these types.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
---
include/linux/lockdep.h | 12 ++++++++++++
kernel/locking/lockdep.c | 34 +++++++++++++++++++++++++++++++---
kernel/locking/lockdep_internals.h | 3 +++
3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1009c47..bc09c85 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -195,6 +195,18 @@ struct lock_list {
struct lock_class *links_to;
struct lock_trace trace;
int distance;
+ /*
+ * This field keeps track of the read-write type of this dependency.
+ *
+ * With L1 -> L2:
+ *
+ * lock_type[0] stores the type of L1, while lock_type[1] stores the
+ * type of L2.
+ */
+ union {
+ int dep_type;
+ u16 lock_type[2];
+ };

/*
* The parent field is used to implement breadth-first search, and the
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index fb6be63..e7eedbf 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1225,7 +1225,7 @@ static struct lock_list *alloc_list_entry(void)
static int add_lock_to_list(struct lock_class *this,
struct lock_class *links_to, struct list_head *head,
unsigned long ip, int distance,
- struct lock_trace *trace)
+ struct lock_trace *trace, int dep_type)
{
struct lock_list *entry;
/*
@@ -1240,6 +1240,8 @@ static int add_lock_to_list(struct lock_class *this,
entry->links_to = links_to;
entry->distance = distance;
entry->trace = *trace;
+ entry->dep_type = dep_type;
+
/*
* Both allocation and removal are done under the graph lock; but
* iteration is under RCU-sched; see look_up_lock_class() and
@@ -1677,6 +1679,30 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
return ret;
}

+static inline int get_dep_type(struct held_lock *lock1, struct held_lock *lock2)
+{
+ /*
+ * With dependency lock1 -> lock2:
+ *
+ * lock_type[0] is lock1, while lock_type[1] is lock2.
+ *
+ * Avoid architectural endianness difference composing dep_type.
+ */
+ u16 type[2] = { lock1->read, lock2->read };
+
+ return *(int *)type;
+}
+
+static inline int get_lock_type1(struct lock_list *lock)
+{
+ return lock->lock_type[0];
+}
+
+static inline int get_lock_type2(struct lock_list *lock)
+{
+ return lock->lock_type[1];
+}
+
/*
* Check that the dependency graph starting at <src> can lead to
* <target> or not. Print an error and return 0 if it does.
@@ -2446,14 +2472,16 @@ static inline void inc_chains(void)
*/
ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
&hlock_class(prev)->locks_after,
- next->acquire_ip, distance, trace);
+ next->acquire_ip, distance, trace,
+ get_dep_type(prev, next));

if (!ret)
return 0;

ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
&hlock_class(next)->locks_before,
- next->acquire_ip, distance, trace);
+ next->acquire_ip, distance, trace,
+ get_dep_type(next, prev));
if (!ret)
return 0;

diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 150ec3f..c287bcb 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -26,6 +26,9 @@ enum lock_usage_bit {
#define LOCK_USAGE_DIR_MASK 2
#define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK))

+#define LOCK_TYPE_BITS 16
+#define LOCK_TYPE_MASK 0xFFFF
+
/*
* Usage-state bitmasks:
*/
--
1.8.3.1