user/sven/linux.git/kernel/cpu.c, branch v4.1.6

Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2015-04-14T20:36:04Z

Pull RCU changes from Ingo Molnar: "The main changes in this cycle were: - changes permitting use of call_rcu() and friends very early in boot, for example, before rcu_init() is invoked. - add in-kernel API to enable and disable expediting of normal RCU grace periods. - improve RCU's handling of (hotplug-) outgoing CPUs. - NO_HZ_FULL_SYSIDLE fixes. - tiny-RCU updates to make it more tiny. - documentation updates. - miscellaneous fixes" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (58 commits) cpu: Provide smpboot_thread_init() on !CONFIG_SMP kernels as well cpu: Defer smpboot kthread unparking until CPU known to scheduler rcu: Associate quiescent-state reports with grace period rcu: Yet another fix for preemption and CPU hotplug rcu: Add diagnostics to grace-period cleanup rcutorture: Default to grace-period-initialization delays rcu: Handle outgoing CPUs on exit from idle loop cpu: Make CPU-offline idle-loop transition point more precise rcu: Eliminate ->onoff_mutex from rcu_node structure rcu: Process offlining and onlining only at grace-period start rcu: Move rcu_report_unblock_qs_rnp() to common code rcu: Rework preemptible expedited bitmask handling rcu: Remove event tracing from rcu_cpu_notify(), used by offline CPUs rcutorture: Enable slow grace-period initializations rcu: Provide diagnostic option to slow down grace-period initialization rcu: Detect stalls caused by failure to propagate up rcu_node tree rcu: Eliminate empty HOTPLUG_CPU ifdef rcu: Simplify sync_rcu_preempt_exp_init() rcu: Put all orphan-callback-related code under same comment rcu: Consolidate offline-CPU callback initialization ...

cpu: Defer smpboot kthread unparking until CPU known to scheduler

2015-04-13T06:25:16Z

Currently, smpboot_unpark_threads() is invoked before the incoming CPU has been added to the scheduler's runqueue structures. This might potentially cause the unparked kthread to run on the wrong CPU, since the correct CPU isn't fully set up yet. That causes a sporadic, hard to debug boot crash triggering on some systems, reported by Borislav Petkov, and bisected down to: 2a442c9c6453 ("x86: Use common outgoing-CPU-notification code") This patch places smpboot_unpark_threads() in a CPU hotplug notifier with priority set so that these kthreads are unparked just after the CPU has been added to the runqueues. Reported-and-tested-by: Borislav Petkov Signed-off-by: Paul E. McKenney Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

clockevents: Cleanup dead cpu explicitely

2015-04-03T06:44:37Z

clockevents_notify() is a leftover from the early design of the clockevents facility. It's really not a notification mechanism, it's a multiplex call. We are way better off to have explicit calls instead of this monstrosity. Split out the cleanup function for a dead cpu and invoke it directly from the cpu down code. Make it conditional on CPU_HOTPLUG as well. Temporary change, will be refined in the future. Signed-off-by: Thomas Gleixner [ Rebased, added clockevents_notify() removal ] Signed-off-by: Rafael J. Wysocki Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1735025.raBZdQHM3m@vostro.rjw.lan Signed-off-by: Ingo Molnar

clockevents: Make tick handover explicit

2015-04-03T06:44:36Z

clockevents_notify() is a leftover from the early design of the clockevents facility. It's really not a notification mechanism, it's a multiplex call. We are way better off to have explicit calls instead of this monstrosity. Split out the tick_handover call and invoke it explicitely from the hotplug code. Temporary solution will be cleaned up in later patches. Signed-off-by: Thomas Gleixner [ Rebase ] Signed-off-by: Rafael J. Wysocki Cc: Peter Zijlstra Cc: John Stultz Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/r/1658173.RkEEILFiQZ@vostro.rjw.lan Signed-off-by: Ingo Molnar

clockevents: Fix cpu_down() race for hrtimer based broadcasting

2015-04-02T12:25:39Z

It was found when doing a hotplug stress test on POWER, that the machine either hit softlockups or rcu_sched stall warnings. The issue was traced to commit: 7cba160ad789 ("powernv/cpuidle: Redesign idle states management") which exposed the cpu_down() race with hrtimer based broadcast mode: 5d1638acb9f6 ("tick: Introduce hrtimer based broadcast") The race is the following: Assume CPU1 is the CPU which holds the hrtimer broadcasting duty before it is taken down. CPU0 CPU1 cpu_down() take_cpu_down() disable_interrupts() cpu_die() while (CPU1 != CPU_DEAD) { msleep(100); switch_to_idle(); stop_cpu_timer(); schedule_broadcast(); } tick_cleanup_cpu_dead() take_over_broadcast() So after CPU1 disabled interrupts it cannot handle the broadcast hrtimer anymore, so CPU0 will be stuck forever. Fix this by explicitly taking over broadcast duty before cpu_die(). This is a temporary workaround. What we really want is a callback in the clockevent device which allows us to do that from the dying CPU by pushing the hrtimer onto a different cpu. That might involve an IPI and is definitely more complex than this immediate fix. Changelog was picked up from: https://lkml.org/lkml/2015/2/16/213 Suggested-by: Thomas Gleixner Tested-by: Nicolas Pitre Signed-off-by: Preeti U. Murthy Cc: linuxppc-dev@lists.ozlabs.org Cc: mpe@ellerman.id.au Cc: nicolas.pitre@linaro.org Cc: peterz@infradead.org Cc: rjw@rjwysocki.net Fixes: http://linuxppc.10917.n7.nabble.com/offlining-cpus-breakage-td88619.html Link: http://lkml.kernel.org/r/20150330092410.24979.59887.stgit@preeti.in.ibm.com [ Merged it to the latest timer tree, renamed the callback, tidied up the changelog. ] Signed-off-by: Ingo Molnar

cpu: Make CPU-offline idle-loop transition point more precise

2015-03-12T22:19:37Z

This commit uses a per-CPU variable to make the CPU-offline code path through the idle loop more precise, so that the outgoing CPU is guaranteed to make it into the idle loop before it is powered off. This commit is in preparation for putting the RCU offline-handling code on this code path, which will eliminate the magic one-jiffy wait that RCU uses as the maximum time for an outgoing CPU to get all the way through the scheduler. The magic one-jiffy wait for incoming CPUs remains a separate issue. Signed-off-by: Paul E. McKenney

hotplugcpu: Avoid deadlocks by waking active_writer

2015-01-06T19:01:14Z

Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and expedited grace periods") introduced another problem that can easily be reproduced by starting/stopping cpus in a loop. E.g.: for i in `seq 5000`; do echo 1 > /sys/devices/system/cpu/cpu1/online echo 0 > /sys/devices/system/cpu/cpu1/online done Will result in: INFO: task /cpu_start_stop:1 blocked for more than 120 seconds. Call Trace: ([<00000000006a028e>] __schedule+0x406/0x91c) [<0000000000130f60>] cpu_hotplug_begin+0xd0/0xd4 [<0000000000130ff6>] _cpu_up+0x3e/0x1c4 [<0000000000131232>] cpu_up+0xb6/0xd4 [<00000000004a5720>] device_online+0x80/0xc0 [<00000000004a57f0>] online_store+0x90/0xb0 ... And a deadlock. Problem is that if the last ref in put_online_cpus() can't get the cpu_hotplug.lock the puts_pending count is incremented, but a sleeping active_writer might never be woken up, therefore never exiting the loop in cpu_hotplug_begin(). This fix removes puts_pending and turns refcount into an atomic variable. We also introduce a wait queue for the active_writer, to avoid possible races and use-after-free. There is no need to take the lock in put_online_cpus() anymore. Can't reproduce it with this fix. Signed-off-by: David Hildenbrand Signed-off-by: Paul E. McKenney

cpu: Avoid puts_pending overflow

2014-11-04T03:21:01Z

A long string of get_online_cpus() with each followed by a put_online_cpu() that fails to acquire cpu_hotplug.lock can result in overflow of the cpu_hotplug.puts_pending counter. Although this is perhaps improbably, a system with absolutely no CPU-hotplug operations will have an arbitrarily long time in which this overflow could occur. This commit therefore adds overflow checks to get_online_cpus() and try_get_online_cpus(). Signed-off-by: Paul E. McKenney Reviewed-by: Pranith Kumar

rcu: More on deadlock between CPU hotplug and expedited grace periods

2014-10-23T14:51:17Z

Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and expedited grace periods) was incomplete. Although it did eliminate deadlocks involving synchronize_sched_expedited()'s acquisition of cpu_hotplug.lock via get_online_cpus(), it did nothing about the similar deadlock involving acquisition of this same lock via put_online_cpus(). This deadlock became apparent with testing involving hibernation. This commit therefore changes put_online_cpus() acquisition of this lock to be conditional, and increments a new cpu_hotplug.puts_pending field in case of acquisition failure. Then cpu_hotplug_begin() checks for this new field being non-zero, and applies any changes to cpu_hotplug.refcount. Reported-by: Jiri Kosina Signed-off-by: Paul E. McKenney Tested-by: Jiri Kosina Tested-by: Borislav Petkov

rcu: Eliminate deadlock between CPU hotplug and expedited grace periods

2014-09-18T23:22:27Z

Currently, the expedited grace-period primitives do get_online_cpus(). This greatly simplifies their implementation, but means that calls to them holding locks that are acquired by CPU-hotplug notifiers (to say nothing of calls to these primitives from CPU-hotplug notifiers) can deadlock. But this is starting to become inconvenient, as can be seen here: https://lkml.org/lkml/2014/8/5/754. The problem in this case is that some developers need to acquire a mutex from a CPU-hotplug notifier, but also need to hold it across a synchronize_rcu_expedited(). As noted above, this currently results in deadlock. This commit avoids the deadlock and retains the simplicity by creating a try_get_online_cpus(), which returns false if the get_online_cpus() reference count could not immediately be incremented. If a call to try_get_online_cpus() returns true, the expedited primitives operate as before. If a call returns false, the expedited primitives fall back to normal grace-period operations. This falling back of course results in increased grace-period latency, but only during times when CPU hotplug operations are actually in flight. The effect should therefore be negligible during normal operation. Signed-off-by: Paul E. McKenney Cc: Josh Triplett Cc: "Rafael J. Wysocki" Tested-by: Lan Tianyu