user/sven/linux.git/kernel/cpu.c, branch v4.12.5

smp/hotplug: Replace BUG_ON and react useful

2017-07-27T22:10:25Z

commit dea1d0f5f1284e3defee4b8484d9fc230686cd42 upstream. The move of the unpark functions to the control thread moved the BUG_ON() there as well. While it made some sense in the idle thread of the upcoming CPU, it's bogus to crash the control thread on the already online CPU, especially as the function has a return value and the callsite is prepared to handle an error return. Replace it with a WARN_ON_ONCE() and return a proper error code. Fixes: 9cd4f1a4e7a8 ("smp/hotplug: Move unparking of percpu threads to the control CPU") Rightfully-ranted-at-by: Linux Torvalds Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

smp/hotplug: Move unparking of percpu threads to the control CPU

2017-07-27T22:10:24Z

commit 9cd4f1a4e7a858849e889a081a99adff83e08e4c upstream. Vikram reported the following backtrace: BUG: scheduling while atomic: swapper/7/0/0x00000002 CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.32-perf+ #680 schedule schedule_hrtimeout_range_clock schedule_hrtimeout wait_task_inactive __kthread_bind_mask __kthread_bind __kthread_unpark kthread_unpark cpuhp_online_idle cpu_startup_entry secondary_start_kernel He analyzed correctly that a parked cpu hotplug thread of an offlined CPU was still on the runqueue when the CPU came back online and tried to unpark it. This causes the thread which invoked kthread_unpark() to call wait_task_inactive() and subsequently schedule() with preemption disabled. His proposed workaround was to "make sure" that a parked thread has scheduled out when the CPU goes offline, so the situation cannot happen. But that's still wrong because the root cause is not the fact that the percpu thread is still on the runqueue and neither that preemption is disabled, which could be simply solved by enabling preemption before calling kthread_unpark(). The real issue is that the calling thread is the idle task of the upcoming CPU, which is not supposed to call anything which might sleep. The moron, who wrote that code, missed completely that kthread_unpark() might end up in schedule(). The solution is simpler than expected. The thread which controls the hotplug operation is waiting for the CPU to call complete() on the hotplug state completion. So the idle task of the upcoming CPU can set its state to CPUHP_AP_ONLINE_IDLE and invoke complete(). This in turn wakes the control task on a different CPU, which then can safely do the unpark and kick the now unparked hotplug thread of the upcoming CPU to complete the bringup to the final target state. Control CPU AP bringup_cpu(); __cpu_up() ------------> bringup_ap(); bringup_wait_for_ap() wait_for_completion(); cpuhp_online_idle(); <------------ complete(); unpark(AP->stopper); unpark(AP->hotplugthread); while(1) do_idle(); kick(AP->hotplugthread); wait_for_completion(); hotplug_thread() run_online_callbacks(); complete(); Fixes: 8df3e07e7f21 ("cpu/hotplug: Let upcoming cpu bring itself fully up") Reported-by: Vikram Mulukutla Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Cc: Sebastian Sewior Cc: Rusty Russell Cc: Tejun Heo Cc: Andrew Morton Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1707042218020.2131@nanos Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

cpu/hotplug: Drop the device lock on error

2017-06-03T07:35:04Z

If a custom CPU target is specified and that one is not available _or_ can't be interrupted then the code returns to userland without dropping a lock as notices by lockdep: |echo 133 > /sys/devices/system/cpu/cpu7/hotplug/target | ================================================ | [ BUG: lock held when returning to user space! ] | ------------------------------------------------ | bash/503 is leaving the kernel with locks still held! | 1 lock held by bash/503: | #0: (device_hotplug_lock){+.+...}, at: [] lock_device_hotplug_sysfs+0x10/0x40 So release the lock then. Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable") Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20170602142714.3ogo25f2wbq6fjpj@linutronix.de

Merge branch 'linus' into locking/core, to pick up fixes

2017-04-14T08:29:40Z

Signed-off-by: Ingo Molnar

lockdep: Fix per-cpu static objects

2017-03-26T13:09:45Z

Since commit 383776fa7527 ("locking/lockdep: Handle statically initialized PER_CPU locks properly") we try to collapse per-cpu locks into a single class by giving them all the same key. For this key we choose the canonical address of the per-cpu object, which would be the offset into the per-cpu area. This has two problems: - there is a case where we run !0 lock->key through static_obj() and expect this to pass; it doesn't for canonical pointers. - 0 is a valid canonical address. Cure both issues by redefining the canonical address as the address of the per-cpu variable on the boot CPU. Since I didn't want to rely on CPU0 being the boot-cpu, or even existing at all, track the boot CPU in a variable. Fixes: 383776fa7527 ("locking/lockdep: Handle statically initialized PER_CPU locks properly") Reported-by: kernel test robot Signed-off-by: Peter Zijlstra (Intel) Tested-by: Borislav Petkov Cc: Sebastian Andrzej Siewior Cc: linux-mm@kvack.org Cc: wfg@linux.intel.com Cc: kernel test robot Cc: LKP Link: http://lkml.kernel.org/r/20170320114108.kbvcsuepem45j5cr@hirez.programming.kicks-ass.net Signed-off-by: Thomas Gleixner

cpu/hotplug: Serialize callback invocations proper

2017-03-14T18:19:27Z

The setup/remove_state/instance() functions in the hotplug core code are serialized against concurrent CPU hotplug, but unfortunately not serialized against themself. As a consequence a concurrent invocation of these function results in corruption of the callback machinery because two instances try to invoke callbacks on remote cpus at the same time. This results in missing callback invocations and initiator threads waiting forever on the completion. The obvious solution to replace get_cpu_online() with cpu_hotplug_begin() is not possible because at least one callsite calls into these functions from a get_online_cpu() locked region. Extend the protection scope of the cpuhp_state_mutex from solely protecting the state arrays to cover the callback invocation machinery as well. Fixes: 5b7aa87e0482 ("cpu/hotplug: Implement setup/removal interface") Reported-and-tested-by: Bart Van Assche Signed-off-by: Sebastian Andrzej Siewior Cc: hpa@zytor.com Cc: mingo@kernel.org Cc: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org Link: http://lkml.kernel.org/r/20170314150645.g4tdyoszlcbajmna@linutronix.de Signed-off-by: Thomas Gleixner

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:35Z

We are going to split out of , which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:35Z

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:29Z

cpu/hotplug: Remove unused but set variable in _cpu_down()

2017-01-18T10:55:09Z

After the recent removal of the hotplug notifiers the variable 'hasdied' in _cpu_down() is set but no longer read, leading to the following GCC warning when building with 'make W=1': kernel/cpu.c:767:7: warning: variable ‘hasdied’ set but not used [-Wunused-but-set-variable] Fix it by removing the variable. Fixes: 530e9b76ae8f ("cpu/hotplug: Remove obsolete cpu hotplug register/unregister functions") Signed-off-by: Tobias Klauser Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: rt@linutronix.de Link: http://lkml.kernel.org/r/20170117143501.20893-1-tklauser@distanz.ch Signed-off-by: Thomas Gleixner