linux/kernel/cpu.c, branch v4.6

cpu/hotplug: Fix rollback during error-out in __cpu_disable()

2016-04-22T07:49:49Z

The recent introduction of the hotplug thread which invokes the callbacks on the plugged cpu, cased the following regression: If takedown_cpu() fails, then we run into several issues: 1) The rollback of the target cpu states is not invoked. That leaves the smp threads and the hotplug thread in disabled state. 2) notify_online() is executed due to a missing skip_onerr flag. That causes that both CPU_DOWN_FAILED and CPU_ONLINE notifications are invoked which confuses quite some notifiers. 3) The CPU_DOWN_FAILED notification is not invoked on the target CPU. That's not an issue per se, but it is inconsistent and in consequence blocks the patches which rely on these states being invoked on the target CPU and not on the controlling cpu. It also does not preserve the strict call order on rollback which is problematic for the ongoing state machine conversion as well. To fix this we add a rollback flag to the remote callback machinery and invoke the rollback including the CPU_DOWN_FAILED notification on the remote cpu. Further mark the notify online state with 'skip_onerr' so we don't get a double invokation. This workaround will go away once we moved the unplug invocation to the target cpu itself. [ tglx: Massaged changelog and moved the CPU_DOWN_FAILED notifiaction to the target cpu ] Fixes: 4cb28ced23c4 ("cpu/hotplug: Create hotplug threads") Reported-by: Heiko Carstens Signed-off-by: Sebastian Andrzej Siewior Cc: linux-s390@vger.kernel.org Cc: rt@linutronix.de Cc: Martin Schwidefsky Cc: Anna-Maria Gleixner Link: http://lkml.kernel.org/r/20160408124015.GA21960@linutronix.de Signed-off-by: Thomas Gleixner

cpu/hotplug: Document states better

2016-03-12T19:57:38Z

Requested-by: Peter Zijlstra Signed-off-by: Thomas Gleixner

cpu/hotplug: Fix smpboot thread ordering

2016-03-10T20:21:59Z

Commit 931ef163309e moved the smpboot thread park/unpark invocation to the state machine. The move of the unpark invocation was premature as it depends on work in progress patches. As a result cpu down can fail, because rcu synchronization in takedown_cpu() eventually requires a functional softirq thread. I never encountered the problem in testing, but 0day testing managed to provide a reliable reproducer. Remove the smpboot_threads_park() call from the state machine for now and put it back into the original place after the rcu synchronization. I'm embarrassed as I knew about the dependency and still managed to get it wrong. Hotplug induced brain melt seems to be the only sensible explanation for that. Fixes: 931ef163309e "cpu/hotplug: Unpark smpboot threads from the state machine" Reported-by: Fengguang Wu Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra

cpu/hotplug: Remove redundant state check

2016-03-06T15:59:42Z

The check for the AP range in cpuhp_is_ap_state() is redundant after commit 8df3e07e7f21 "cpu/hotplug: Let upcoming cpu bring itself fully up" because all states above CPUHP_BRINGUP_CPU are invoked on the hotplugged cpu. Remove it. Reported-by: Richard Cochran Signed-off-by: Thomas Gleixner

cpu/hotplug: Plug death reporting race

2016-03-03T09:52:10Z

Paul noticed that the conversion of the death reporting introduced a race where the outgoing cpu might be delayed after waking the controll processor, so it might not be able to call rcu_report_dead() before being physically removed, leading to RCU stalls. We cant call complete after rcu_report_dead(), so instead of going back to busy polling, simply issue a function call to do the completion. Fixes: 27d50c7eeb0f "rcu: Make CPU_DYING_IDLE an explicit call" Reported-by: Paul E. McKenney Link: http://lkml.kernel.org/r/20160302201127.GA23440@linux.vnet.ibm.com Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra

rcu: Make CPU_DYING_IDLE an explicit call

2016-03-01T19:36:58Z

Make the RCU CPU_DYING_IDLE callback an explicit function call, so it gets invoked at the proper place. Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Rik van Riel Cc: Rafael Wysocki Cc: "Srivatsa S. Bhat" Cc: Peter Zijlstra Cc: Arjan van de Ven Cc: Sebastian Siewior Cc: Rusty Russell Cc: Steven Rostedt Cc: Oleg Nesterov Cc: Tejun Heo Cc: Andrew Morton Cc: Paul McKenney Cc: Linus Torvalds Cc: Paul Turner Link: http://lkml.kernel.org/r/20160226182341.870167933@linutronix.de Signed-off-by: Thomas Gleixner

cpu/hotplug: Make wait for dead cpu completion based

2016-03-01T19:36:58Z

Kill the busy spinning on the control side and just wait for the hotplugged cpu to tell that it reached the dead state. Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Rik van Riel Cc: Rafael Wysocki Cc: "Srivatsa S. Bhat" Cc: Peter Zijlstra Cc: Arjan van de Ven Cc: Sebastian Siewior Cc: Rusty Russell Cc: Steven Rostedt Cc: Oleg Nesterov Cc: Tejun Heo Cc: Andrew Morton Cc: Paul McKenney Cc: Linus Torvalds Cc: Paul Turner Link: http://lkml.kernel.org/r/20160226182341.776157858@linutronix.de Signed-off-by: Thomas Gleixner

cpu/hotplug: Let upcoming cpu bring itself fully up

2016-03-01T19:36:57Z

Let the upcoming cpu kick the hotplug thread and let itself complete the bringup. That way the controll side can just wait for the completion or later when we made the hotplug machinery async not care at all. Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Rik van Riel Cc: Rafael Wysocki Cc: "Srivatsa S. Bhat" Cc: Peter Zijlstra Cc: Arjan van de Ven Cc: Sebastian Siewior Cc: Rusty Russell Cc: Steven Rostedt Cc: Oleg Nesterov Cc: Tejun Heo Cc: Andrew Morton Cc: Paul McKenney Cc: Linus Torvalds Cc: Paul Turner Link: http://lkml.kernel.org/r/20160226182341.697655464@linutronix.de Signed-off-by: Thomas Gleixner

cpu/hotplug: Move online calls to hotplugged cpu

2016-03-01T19:36:57Z

Let the hotplugged cpu invoke the setup/teardown callbacks (CPU_ONLINE/CPU_DOWN_PREPARE) itself. Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Rik van Riel Cc: Rafael Wysocki Cc: "Srivatsa S. Bhat" Cc: Peter Zijlstra Cc: Arjan van de Ven Cc: Sebastian Siewior Cc: Rusty Russell Cc: Steven Rostedt Cc: Oleg Nesterov Cc: Tejun Heo Cc: Andrew Morton Cc: Paul McKenney Cc: Linus Torvalds Cc: Paul Turner Link: http://lkml.kernel.org/r/20160226182341.536364371@linutronix.de Signed-off-by: Thomas Gleixner

cpu/hotplug: Create hotplug threads

2016-03-01T19:36:56Z

In order to let the hotplugged cpu take care of the setup/teardown, we need a seperate hotplug thread. Signed-off-by: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: Rik van Riel Cc: Rafael Wysocki Cc: "Srivatsa S. Bhat" Cc: Peter Zijlstra Cc: Arjan van de Ven Cc: Sebastian Siewior Cc: Rusty Russell Cc: Steven Rostedt Cc: Oleg Nesterov Cc: Tejun Heo Cc: Andrew Morton Cc: Paul McKenney Cc: Linus Torvalds Cc: Paul Turner Link: http://lkml.kernel.org/r/20160226182341.454541272@linutronix.de Signed-off-by: Thomas Gleixner