On Mon, Jan 02, 2023 at 08:43:10AM -0800, Davidlohr Bueso wrote: > On Sun, 01 Jan 2023, Joel Fernandes (Google) wrote: > > > During shutdown of rcutorture, the shutdown thread in > > rcu_torture_cleanup() calls torture_cleanup_begin() which sets fullstop > > to FULLSTOP_RMMOD. This is enough to cause the rcutorture threads for > > readers and fakewriters to breakout of their main while loop and start > > shutting down. > > > > Once out of their main loop, they then call torture_kthread_stopping() > > which in turn waits for kthread_stop() to be called, however > > rcu_torture_cleanup() has not even called kthread_stop() on those > > threads yet, it does that a bit later. However, before it gets a chance > > to do so, torture_kthread_stopping() calls > > schedule_timeout_interruptible(1) in a tight loop. Tracing confirmed > > this makes the timer softirq constantly execute timer callbacks, while > > never returning back to the softirq exit path and is essentially "locked > > up" because of that. If the softirq preempts the shutdown thread, > > kthread_stop() may never be called. > > > > This commit improves the situation dramatically, by increasing timeout > > passed to schedule_timeout_interruptible() 1/20th of a second. This > > causes the timer softirq to not lock up a CPU and everything works fine. > > Testing has shown 100 runs of TREE07 passing reliably, which was not the > > case before because of RCU stalls. > > > > Cc: Paul McKenney <paulmck@xxxxxxxxxx> > > Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> > > Cc: Zhouyi Zhou <zhouzhouyi@xxxxxxxxx> > > Cc: <stable@xxxxxxxxxxxxxxx> # 6.0.x > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx> Queued for further review and testing, thank you all! One thing still puzzles me. Assuming HZ=1000 and given 16 CPUs, each timer hander must have consumed many tens of microseconds in order to keep the system busy, which seems a bit longer than it should be. Or am I underestimating the number of tasks involved? Thanx, Paul
