| Message ID | 20141208085405.730577a3@gandalf.local.home (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On 12/08/2014 09:54 PM, Steven Rostedt wrote: > On Mon, 8 Dec 2014 14:27:01 +1100 > Anton Blanchard <anton@samba.org> wrote: > >> I have a busy ppc64le KVM box where guests sometimes hit the infamous >> "kernel BUG at kernel/smpboot.c:134!" issue during boot: >> >> BUG_ON(td->cpu != smp_processor_id()); >> >> Basically a per CPU hotplug thread scheduled on the wrong CPU. The oops >> output confirms it: >> >> CPU: 0 >> Comm: watchdog/130 >> >> The issue is in kthread_bind where we set the cpus_allowed mask, but do >> not touch task_thread_info(p)->cpu. The scheduler assumes the previously >> scheduled CPU is in the cpus_allowed mask, but in this case we are >> moving a thread to another CPU so it is not. >> > > Does this happen always on boot up, and always with the watchdog thread? > > I followed the logic that starts the watchdog threads. > > watchdog_enable_all_cpus() > smpboot_register_percpu-thread() { > > for_each_online_cpu(cpu) { ... } > > Where watchdog_enable_all_cpus() can be called by > lockup_detector_init() before SMP is started, but also by > proc_dowatchdog() which is called by the sysctl commands (after SMP is > up and running). > > I noticed there's no "get_online_cpus()" anywhere, although the > unregister_percpu_thread() has it. Is it possible that we created a > thread on a CPU that wasn't fully online yet? > > Perhaps the following patch is needed? Even if this isn't the solution > to this bug, it is probably needed as watchdog_enable_all_cpus() can be > called after boot up too. > > -- Steve Hi, Steven, tglx See this https://lkml.org/lkml/2014/7/30/804 "[PATCH] smpboot: add missing get_online_cpus() when register" Thanks, Lai > > diff --git a/kernel/smpboot.c b/kernel/smpboot.c > index eb89e1807408..60d35ac5d3f1 100644 > --- a/kernel/smpboot.c > +++ b/kernel/smpboot.c > @@ -279,6 +279,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) > unsigned int cpu; > int ret = 0; > > + get_online_cpus(); > mutex_lock(&smpboot_threads_lock); > for_each_online_cpu(cpu) { > ret = __smpboot_create_thread(plug_thread, cpu); > @@ -291,6 +292,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) > list_add(&plug_thread->list, &hotplug_threads); > out: > mutex_unlock(&smpboot_threads_lock); > + put_online_cpus(); > return ret; > } > EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > . >
diff --git a/kernel/smpboot.c b/kernel/smpboot.c index eb89e1807408..60d35ac5d3f1 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -279,6 +279,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) unsigned int cpu; int ret = 0; + get_online_cpus(); mutex_lock(&smpboot_threads_lock); for_each_online_cpu(cpu) { ret = __smpboot_create_thread(plug_thread, cpu); @@ -291,6 +292,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) list_add(&plug_thread->list, &hotplug_threads); out: mutex_unlock(&smpboot_threads_lock); + put_online_cpus(); return ret; } EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);