On Wed, Jul 12, 2017 at 10:44:54AM -0500, Christopher Lameter wrote: > On Wed, 7 Jun 2017, Andre Wild wrote: > > > I'm currently seeing the following message running kernel version 4.11.0. > > It looks like it was introduced with the patch > > 4037d452202e34214e8a939fa5621b2b3bbb45b7. > > A 2007 patch? At that point we did not have __this_cpu_read() nor > refresh_cpu_vmstats.... Is this on s390 or some such architecture? It is on s390, but after I looked into the code a bit deeper the mentioned patch doesn't seem to be the problem. My initial thought was a missing preempt_disable() / preempt_enable() pair, but that can't be the problem, since the code is executed on a per-cpu workqueue. > > Can you please take a look at this problem? > > Could you give me a bit more context? > > > > [Tue Jun 6 15:27:03 2017] BUG: using __this_cpu_read() in preemptible > > [00000000] code: mm_percpu_wq/7 > > [Tue Jun 6 15:27:03 2017] caller is refresh_cpu_vm_stats+0x198/0x3d8 > > [Tue Jun 6 15:27:03 2017] CPU: 0 PID: 7 Comm: mm_percpu_wq Tainted: G > > W 4.11.0-20170529.0.ae409ab.224a322.fc25.s390xdefault #1 > > [Tue Jun 6 15:27:03 2017] Workqueue: mm_percpu_wq vmstat_update > > It is run in preemptible mode but this from a kworker > context so the processor cannot change (see vmstat_refresh()). > > Even on s390 or so this should be fine. Yes, it *should* be fine. The only unusual thing here is that this happens during quite a lot of cpu hotplug operations. So even though the workqueue code should be able to handle cpu hotplug correctly, my best guess is that current->cpus_allowed is not cpumask_of(this_cpu) for some reason. That would be this check within lib/smp_processor_id.c:check_preemption_disabled() if (cpumask_equal(¤t->cpus_allowed, cpumask_of(this_cpu))) goto out; I changed the code to simply panic, so I can look into a dump to figure out what actually does cause the warning. As soon as Andre finds some time to reproduce this we will come back to you. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
