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Date: Wed, 11 Apr 2018 21:50:56 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Andrea Parri <parri.andrea@...il.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Boqun Feng <boqun.feng@...il.com>
Subject: [RFC tip/locking/lockdep v6 06/20] lockdep: Introduce lock_list::dep
To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four types of
dependencies:
* Non-recursive -> Non-recursive dependencies: NN
e.g. write_lock(prev) held and try to acquire write_lock(next),
which can be represented as "prev -(NN)-> next".
* Recursive -> Non-recursive dependencies: RN
e.g. read_lock(prev) held and try to acquire write_lock(next),
which can be represented as "prev -(RN)-> next".
* Non-recursive -> recursive dependencies: NR
e.g. write_lock(prev) held and try to acquire read_lock(next),
which can be represented as "prev -(NR)-> next".
* Recursive -> recursive dependencies: RR
e.g. read_lock(prev) held and try to acquire read_lock(next),
which can be represented as "prev -(RR)-> next".
So we use 4 bits for the presence of each type in lock_list::dep. Helper
functions and marcos are also introduced to convert a pair of locks into
lock_list::dep bit and maintain the addition of different types of
dependencies.
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
include/linux/lockdep.h | 2 ++
kernel/locking/lockdep.c | 76 +++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 74 insertions(+), 4 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index d2af32387aaa..cbd257f62877 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -187,6 +187,8 @@ struct lock_list {
struct lock_class *class;
struct stack_trace trace;
u16 distance;
+ /* bitmap of different dependencies from head to this */
+ u8 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 1806060c88ce..0892855b6c57 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -859,7 +859,7 @@ static struct lock_list *alloc_list_entry(void)
* Add a new dependency to the head of the list:
*/
static int add_lock_to_list(struct lock_class *this, struct list_head *head,
- unsigned long ip, u16 distance,
+ unsigned long ip, u16 distance, u8 dep,
struct stack_trace *trace)
{
struct lock_list *entry;
@@ -872,6 +872,7 @@ 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;
/*
@@ -1012,6 +1013,41 @@ static inline bool bfs_error(enum bfs_result res)
return res < 0;
}
+/*
+ * DEP_*_BIT in lock_list::dep
+ *
+ * For dependency @prev -> @next:
+ *
+ * RR: both @prev and @next are recursive read locks, i.e. ->read == 2.
+ * NR: @prev is a non-recursive and @next is recursive.
+ * RN: @prev is recursive and @next is non-recursive.
+ * NN: both @prev and @next are non-recursive.
+ *
+ * Note that we define the value of DEP_*_BITs so that:
+ * bit0 is prev->read != 2
+ * bit1 is next->read != 2
+ */
+#define DEP_RR_BIT (0 + (0 << 1)) /* 0 */
+#define DEP_NR_BIT (1 + (0 << 1)) /* 1 */
+#define DEP_RN_BIT (0 + (1 << 1)) /* 2 */
+#define DEP_NN_BIT (1 + (1 << 1)) /* 3 */
+
+#define DEP_RR_MASK (1U << (DEP_RR_BIT))
+#define DEP_NR_MASK (1U << (DEP_NR_BIT))
+#define DEP_RN_MASK (1U << (DEP_RN_BIT))
+#define DEP_NN_MASK (1U << (DEP_NN_BIT))
+
+static inline unsigned int
+__calc_dep_bit(struct held_lock *prev, struct held_lock *next)
+{
+ return (prev->read != 2) + ((next->read != 2) << 1);
+}
+
+static inline u8 calc_dep(struct held_lock *prev, struct held_lock *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),
@@ -1921,7 +1957,35 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
if (entry->class == hlock_class(next)) {
if (distance == 1)
entry->distance = 1;
- return 1;
+ entry->dep |= calc_dep(prev, next);
+
+ /*
+ * Also, update the reverse dependency in @next's
+ * ->locks_before list.
+ *
+ * Here we reuse @entry as the cursor, which is fine
+ * because we won't go to the next iteration of the
+ * outer loop:
+ *
+ * For normal cases, we return in the inner loop.
+ *
+ * If we fail to return, we have inconsistency, i.e.
+ * <prev>::locks_after contains <next> while
+ * <next>::locks_before doesn't contain <prev>. In
+ * that case, we return after the inner and indicate
+ * something is wrong.
+ */
+ 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, prev);
+ return 1;
+ }
+ }
+
+ /* <prev> is not found in <next>::locks_before */
+ return 0;
}
}
@@ -1948,14 +2012,18 @@ 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, next),
+ 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, prev),
+ trace);
if (!ret)
return 0;
--
2.16.2
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