[RFC PATCH] kernel/locking: introduce stack_handle for tracing the callstack

[zhaoyang.huang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

When deadlock happens, sometimes it is hard to know how the owner get the lock
especially the owner is running when snapshot(ramdump). Introduce stack_handle
to record the trace.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 include/linux/rwsem.h  |  9 ++++++++-
 kernel/locking/rwsem.c | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index efa5c32..ad4c591 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -16,6 +16,11 @@
 #include <linux/atomic.h>
 #include <linux/err.h>
 
+#define CONFIG_TRACE_RWSEMS
+#ifdef CONFIG_TRACE_RWSEMS
+typedef u32 depot_stack_handle_t;
+#endif
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define __RWSEM_DEP_MAP_INIT(lockname)			\
 	.dep_map = {					\
@@ -31,7 +36,6 @@
 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 #include <linux/osq_lock.h>
 #endif
-
 /*
  * For an uncontended rwsem, count and owner are the only fields a task
  * needs to touch when acquiring the rwsem. So they are put next to each
@@ -60,6 +64,9 @@ struct rw_semaphore {
 #ifdef CONFIG_DEBUG_RWSEMS
 	void *magic;
 #endif
+#ifdef CONFIG_TRACE_RWSEMS
+	depot_stack_handle_t trace_handle;
+#endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 4487359..a12766e 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -28,6 +28,7 @@
 #include <linux/rwsem.h>
 #include <linux/atomic.h>
 #include <trace/events/lock.h>
+#include <linux/stacktrace.h>
 
 #ifndef CONFIG_PREEMPT_RT
 #include "lock_events.h"
@@ -74,6 +75,7 @@
 		list_empty(&(sem)->wait_list) ? "" : "not "))	\
 			debug_locks_off();			\
 	} while (0)
+#define MAX_TRACE		16
 #else
 # define DEBUG_RWSEMS_WARN_ON(c, sem)
 #endif
@@ -174,6 +176,9 @@ static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
 		(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
 
 	atomic_long_set(&sem->owner, val);
+#ifdef CONFIG_TRACE_RWSEMS
+	sem->trace_handle = owner ? set_track_prepare() : NULL;
+#endif
 }
 
 static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
@@ -397,6 +402,19 @@ enum rwsem_wake_type {
 	return false;
 }
 
+#ifdef CONFIG_TRACE_RWSEMS
+static inline depot_stack_handle_t set_track_prepare(void)
+{
+	depot_stack_handle_t trace_handle;
+	unsigned long entries[MAX_TRACE];
+	unsigned int nr_entries;
+
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
+	trace_handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
+
+	return trace_handle;
+}
+#endif
 /*
  * handle the lock release when processes blocked on it that can now run
  * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
-- 
1.9.1