From: "Joel Fernandes (Google)" joel@joelfernandes.org

During rcutorture shutdown, the rcu_torture_cleanup() function calls torture_cleanup_begin(), which sets the fullstop global variable to FULLSTOP_RMMOD. This causes the rcutorture threads for readers and fakewriters to exit all of their "while" loops and start shutting down.

They then call torture_kthread_stopping(), which in turn waits for kthread_stop() to be called. However, rcu_torture_cleanup() has not yet called kthread_stop() on those threads, and before it gets a chance to do so, multiple instances of torture_kthread_stopping() invoke schedule_timeout_interruptible(1) in a tight loop. Tracing confirms that TIMER_SOFTIRQ can then continuously execute timer callbacks. If that TIMER_SOFTIRQ preempts the task executing rcu_torture_cleanup(), that task might never invoke kthread_stop().

This commit improves this situation by increasing the timeout passed to schedule_timeout_interruptible() from one jiffy to 1/20th of a second. This change prevents TIMER_SOFTIRQ from monopolizing its CPU, thus allowing rcu_torture_cleanup() to carry out the needed kthread_stop() invocations. Testing has shown 100 runs of TREE07 passing reliably, as oppose to the tens-of-percent failure rates seen beforehand.

Cc: Paul McKenney paulmck@kernel.org Cc: Frederic Weisbecker fweisbec@gmail.com Cc: Zhouyi Zhou zhouzhouyi@gmail.com Cc: stable@vger.kernel.org # 6.0.x Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org Tested-by: Zhouyi Zhou zhouzhouyi@gmail.com Reviewed-by: Davidlohr Bueso dave@stgolabs.net Signed-off-by: Paul E. McKenney paulmck@kernel.org --- kernel/torture.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/torture.c b/kernel/torture.c index 29afc62f2bfec..1a0519b836ac9 100644 --- a/kernel/torture.c +++ b/kernel/torture.c @@ -915,7 +915,7 @@ void torture_kthread_stopping(char *title) VERBOSE_TOROUT_STRING(buf); while (!kthread_should_stop()) { torture_shutdown_absorb(title); - schedule_timeout_uninterruptible(1); + schedule_timeout_uninterruptible(HZ / 20); } } EXPORT_SYMBOL_GPL(torture_kthread_stopping);