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Subject[RFC tip/locking v2 04/13] lockdep: Introduce lock_list::dep
Date
To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four kinds of
dependencies:

* Non-recursive -> Non-recursive dependencies(NN)
e.g. write_lock(prev) -> write_lock(next)

* Recursive -> Non-recursive dependencies(RN)
e.g. read_lock(prev) -> write_lock(next);

* Non-recursive -> recursive dependencies(NR)
e.g. write_lock(prev) -> read_lock(next);

* Recursive -> recursive dependencies(RR)
e.g. read_lock(prev) -> read_lock(next);

Given a pair of two locks, four kinds of dependencies could all exist
between them, so we use 4 bit for the presence of each kind(stored in
lock_list::dep).

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
include/linux/lockdep.h | 2 ++
kernel/locking/lockdep.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index bfa8e0b0d6f1..35b3fc0d6793 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -192,6 +192,8 @@ struct lock_list {
struct lock_class *class;
struct stack_trace trace;
int distance;
+ /* bitmap of different dependencies from head to this */
+ u16 dep;

/*
* 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 86ef7ea9f79f..1220dab7a506 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -884,6 +884,7 @@ static int add_lock_to_list(struct lock_class *this, struct list_head *head,
return 0;

entry->class = this;
+ entry->dep = dep;
entry->distance = distance;
entry->trace = *trace;
/*
@@ -1024,6 +1025,33 @@ static inline bool bfs_error(enum bfs_result res)
return res < 0;
}

+#define DEP_NN_BIT 0
+#define DEP_RN_BIT 1
+#define DEP_NR_BIT 2
+#define DEP_RR_BIT 3
+
+#define DEP_NN_MASK (1U << (DEP_NN_BIT))
+#define DEP_RN_MASK (1U << (DEP_RN_BIT))
+#define DEP_NR_MASK (1U << (DEP_NR_BIT))
+#define DEP_RR_MASK (1U << (DEP_RR_BIT))
+
+static inline unsigned int __calc_dep_bit(int prev, int next)
+{
+ if (prev == 2 && next != 2)
+ return DEP_RN_BIT;
+ if (prev != 2 && next == 2)
+ return DEP_NR_BIT;
+ if (prev == 2 && next == 2)
+ return DEP_RR_BIT;
+ else
+ return DEP_NN_BIT;
+}
+
+static inline unsigned int calc_dep(int prev, int next)
+{
+ return 1U << __calc_dep_bit(prev, next);
+}
+
static enum bfs_result __bfs(struct lock_list *source_entry,
void *data,
int (*match)(struct lock_list *entry, void *data),
@@ -1951,6 +1979,16 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
if (entry->class == hlock_class(next)) {
if (distance == 1)
entry->distance = 1;
+ entry->dep |= calc_dep(prev->read, next->read);
+ }
+ }
+
+ /* Also, update the reverse dependency in @next's ->locks_before list */
+ list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
+ if (entry->class == hlock_class(prev)) {
+ if (distance == 1)
+ entry->distance = 1;
+ entry->dep |= calc_dep(next->read, prev->read);
return 1;
}
}
@@ -1978,14 +2016,18 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
ret = add_lock_to_list(hlock_class(next),
&hlock_class(prev)->locks_after,
- next->acquire_ip, distance, trace);
+ next->acquire_ip, distance,
+ calc_dep(prev->read, next->read),
+ trace);

if (!ret)
return 0;

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

--
2.14.1
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