[PATCH v4 04/24] dept: Add a API for skipping dependency check temporarily

[Byungchul Park]

Dept would skip check for dmaps marked by dept_map_nocheck() permanently.
However, sometimes it needs to skip check for some dmaps temporarily and
back to normal, for instance, lock acquisition with a nest lock.

Lock usage check with regard to nest lock could be performed by Lockdep,
however, dependency check is not necessary for that case. So prepared
for it by adding two new APIs, dept_skip() and dept_unskip_if_skipped().

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
 include/linux/dept.h     |  9 +++++++++
 include/linux/dept_sdt.h |  2 +-
 include/linux/lockdep.h  |  4 +++-
 kernel/dependency/dept.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/include/linux/dept.h b/include/linux/dept.h
index c3fb3cf..c0bbb8e 100644
--- a/include/linux/dept.h
+++ b/include/linux/dept.h
@@ -352,6 +352,11 @@ struct dept_map {
 	unsigned int			wgen;
 
 	/*
+	 * for skipping dependency check temporarily
+	 */
+	atomic_t			skip_cnt;
+
+	/*
 	 * whether this map should be going to be checked or not
 	 */
 	bool				nocheck;
@@ -444,6 +449,8 @@ struct dept_task {
 extern void dept_ask_event(struct dept_map *m);
 extern void dept_event(struct dept_map *m, unsigned long e_f, unsigned long ip, const char *e_fn);
 extern void dept_ecxt_exit(struct dept_map *m, unsigned long ip);
+extern void dept_skip(struct dept_map *m);
+extern bool dept_unskip_if_skipped(struct dept_map *m);
 
 /*
  * for users who want to manage external keys
@@ -475,6 +482,8 @@ struct dept_task {
 #define dept_ask_event(m)			do { } while (0)
 #define dept_event(m, e_f, ip, e_fn)		do { (void)(e_fn); } while (0)
 #define dept_ecxt_exit(m, ip)			do { } while (0)
+#define dept_skip(m)				do { } while (0)
+#define dept_unskip_if_skipped(m)		(false)
 #define dept_key_init(k)			do { (void)(k); } while (0)
 #define dept_key_destroy(k)			do { (void)(k); } while (0)
 #endif
diff --git a/include/linux/dept_sdt.h b/include/linux/dept_sdt.h
index 375c4c3..e9d558d 100644
--- a/include/linux/dept_sdt.h
+++ b/include/linux/dept_sdt.h
@@ -13,7 +13,7 @@
 #include <linux/dept.h>
 
 #ifdef CONFIG_DEPT
-#define DEPT_SDT_MAP_INIT(dname)	{ .name = #dname }
+#define DEPT_SDT_MAP_INIT(dname)	{ .name = #dname, .skip_cnt = ATOMIC_INIT(0) }
 
 /*
  * SDT(Single-event Dependency Tracker) APIs
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index c56f6b6..c1a56fe 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -488,7 +488,9 @@ enum xhlock_context_t {
  */
 #define STATIC_DEPT_MAP_INIT(_name, _key) .dmap = {		\
 	.name = (_name),					\
-	.keys = NULL },
+	.keys = NULL,						\
+	.skip_cnt = ATOMIC_INIT(0),				\
+	},
 #else
 #define STATIC_DEPT_MAP_INIT(_name, _key)
 #endif
diff --git a/kernel/dependency/dept.c b/kernel/dependency/dept.c
index ec3f131..3f22c5b 100644
--- a/kernel/dependency/dept.c
+++ b/kernel/dependency/dept.c
@@ -1943,6 +1943,7 @@ void dept_map_init(struct dept_map *m, struct dept_key *k, int sub,
 	m->name = n;
 	m->wgen = 0U;
 	m->nocheck = false;
+	atomic_set(&m->skip_cnt, 0);
 exit:
 	dept_exit(flags);
 }
@@ -1963,6 +1964,7 @@ void dept_map_reinit(struct dept_map *m)
 
 	clean_classes_cache(&m->keys_local);
 	m->wgen = 0U;
+	atomic_set(&m->skip_cnt, 0);
 
 	dept_exit(flags);
 }
@@ -2346,6 +2348,53 @@ void dept_ecxt_exit(struct dept_map *m, unsigned long ip)
 }
 EXPORT_SYMBOL_GPL(dept_ecxt_exit);
 
+void dept_skip(struct dept_map *m)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+
+	if (READ_ONCE(dept_stop) || dt->recursive)
+		return;
+
+	if (m->nocheck)
+		return;
+
+	flags = dept_enter();
+
+	atomic_inc(&m->skip_cnt);
+
+	dept_exit(flags);
+}
+EXPORT_SYMBOL_GPL(dept_skip);
+
+/*
+ * Return true if successfully unskip, otherwise false.
+ */
+bool dept_unskip_if_skipped(struct dept_map *m)
+{
+	struct dept_task *dt = dept_task();
+	unsigned long flags;
+	bool ret = false;
+
+	if (READ_ONCE(dept_stop) || dt->recursive)
+		return false;
+
+	if (m->nocheck)
+		return false;
+
+	flags = dept_enter();
+
+	if (!atomic_read(&m->skip_cnt))
+		goto exit;
+
+	atomic_dec(&m->skip_cnt);
+	ret = true;
+exit:
+	dept_exit(flags);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dept_unskip_if_skipped);
+
 void dept_task_exit(struct task_struct *t)
 {
 	struct dept_task *dt = &t->dept_task;
-- 
1.9.1