From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@linux.vnet.ibm.com (Paul E. McKenney) Date: Mon, 21 Aug 2017 17:38:17 -0700 Subject: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this? In-Reply-To: <20170821105258.191d04b1@roar.ozlabs.ibm.com> References: <20170802172555.0000468a@huawei.com> <20170815154743.GK7017@linux.vnet.ibm.com> <87wp63smwn.fsf@concordia.ellerman.id.au> <20170816125617.GY7017@linux.vnet.ibm.com> <20170816162731.GA22978@linux.vnet.ibm.com> <20170820144553.2ab2727b@ppc64le> <20170820230040.706b62ac@roar.ozlabs.ibm.com> <20170820183514.GM11320@linux.vnet.ibm.com> <20170820211429.GA27111@linux.vnet.ibm.com> <20170821105258.191d04b1@roar.ozlabs.ibm.com> Message-ID: <20170822003817.GU11320@linux.vnet.ibm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Aug 21, 2017 at 10:52:58AM +1000, Nicholas Piggin wrote: > On Sun, 20 Aug 2017 14:14:29 -0700 > "Paul E. McKenney" wrote: > > > On Sun, Aug 20, 2017 at 11:35:14AM -0700, Paul E. McKenney wrote: > > > On Sun, Aug 20, 2017 at 11:00:40PM +1000, Nicholas Piggin wrote: > > > > On Sun, 20 Aug 2017 14:45:53 +1000 > > > > Nicholas Piggin wrote: > > > > > > > > > On Wed, 16 Aug 2017 09:27:31 -0700 > > > > > "Paul E. McKenney" wrote: > > > > > > On Wed, Aug 16, 2017 at 05:56:17AM -0700, Paul E. McKenney wrote: > > > > > > > > > > > > Thomas, John, am I misinterpreting the timer trace event messages? > > > > > > > > > > So I did some digging, and what you find is that rcu_sched seems to do a > > > > > simple scheudle_timeout(1) and just goes out to lunch for many seconds. > > > > > The process_timeout timer never fires (when it finally does wake after > > > > > one of these events, it usually removes the timer with del_timer_sync). > > > > > > > > > > So this patch seems to fix it. Testing, comments welcome. > > > > > > > > Okay this had a problem of trying to forward the timer from a timer > > > > callback function. > > > > > > > > This was my other approach which also fixes the RCU warnings, but it's > > > > a little more complex. I reworked it a bit so the mod_timer fast path > > > > hopefully doesn't have much more overhead (actually by reading jiffies > > > > only when needed, it probably saves a load). > > > > > > Giving this one a whirl! > > > > No joy here, but then again there are other reasons to believe that I > > am seeing a different bug than Dave and Jonathan are. > > > > OK, not -entirely- without joy -- 10 of 14 runs were error-free, which > > is a good improvement over 0 of 84 for your earlier patch. ;-) But > > not statistically different from what I see without either patch. > > > > But no statistical difference compared to without patch, and I still > > see the "rcu_sched kthread starved" messages. For whatever it is worth, > > by the way, I also see this: "hrtimer: interrupt took 5712368 ns". > > Hmmm... I am also seeing that without any of your patches. Might > > be hypervisor preemption, I guess. > > Okay it makes the warnings go away for me, but I'm just booting then > leaving the system idle. You're doing some CPU hotplug activity? Yes, along with rcutorture, so a very different workload. Thanx, Paul