linux-kernel - [PATCH tip/core/rcu 03/28] locktorture: Track time of last ->writeunlock()

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Date:   Thu,  5 Nov 2020 15:46:54 -0800
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH tip/core/rcu 03/28] locktorture: Track time of last ->writeunlock()

From: "Paul E. McKenney" <paulmck@...nel.org>

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.

Cc: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 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");
-- 
2.9.5