[tip: core/rcu] locktorture: Track time of last ->writeunlock()

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     3480d6774f07341e3e1cf3114f58bef98ea58ae0
Gitweb:        https://git.kernel.org/tip/3480d6774f07341e3e1cf3114f58bef98ea58ae0
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Sun, 30 Aug 2020 21:48:23 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Fri, 06 Nov 2020 17:13:29 -08:00

locktorture: Track time of last ->writeunlock()

This commit adds a last_lock_release variable that tracks the time of
the last ->writeunlock() call, which allows easier diagnosing of lock
hangs when using a kernel debugger.

Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/locking/locktorture.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 62d215b..316531d 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -60,6 +60,7 @@ static struct task_struct **reader_tasks;
 
 static bool lock_is_write_held;
 static bool lock_is_read_held;
+static unsigned long last_lock_release;
 
 struct lock_stress_stats {
 	long n_lock_fail;
@@ -632,6 +633,7 @@ static int lock_torture_writer(void *arg)
 		lwsp->n_lock_acquired++;
 		cxt.cur_ops->write_delay(&rand);
 		lock_is_write_held = false;
+		WRITE_ONCE(last_lock_release, jiffies);
 		cxt.cur_ops->writeunlock();
 
 		stutter_wait("lock_torture_writer");