user/sven/linux.git/kernel/cpu.c, branch v3.18.28

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

sched: Rework check_for_tasks()

2014-07-05T09:17:45Z

1) Iterate thru all of threads in the system. Check for all threads, not only for group leaders. 2) Check for p->on_rq instead of p->state and cputime. Preempted task in !TASK_RUNNING state OR just created task may be queued, that we want to be reported too. 3) Use read_lock() instead of write_lock(). This function does not change any structures, and read_lock() is enough. Signed-off-by: Kirill Tkhai Reviewed-by: Srikar Dronamraju Cc: Andrew Morton Cc: Ben Segall Cc: Fabian Frederick Cc: Gautham R. Shenoy Cc: Konstantin Khorenko Cc: Linus Torvalds Cc: Michael wang Cc: Mike Galbraith Cc: Paul Gortmaker Cc: Paul Turner Cc: Rafael J. Wysocki Cc: Srivatsa S. Bhat Cc: Todd E Brandt Cc: Toshi Kani Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1403684395.3462.44.camel@tkhai Signed-off-by: Ingo Molnar

Merge tag 'pm+acpi-3.16-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

2014-06-12T20:14:19Z

Pull more ACPI and power management updates from Rafael Wysocki: "These are fixups on top of the previous PM+ACPI pull request, regression fixes (ACPI hotplug, cpufreq ppc-corenet), other bug fixes (ACPI reset, cpufreq), new PM trace points for system suspend profiling and a copyright notice update. Specifics: - I didn't remember correctly that the Hans de Goede's ACPI video patches actually didn't flip the video.use_native_backlight default, although we had discussed that and decided to do that. Since I said we would do that in the previous PM+ACPI pull request, make that change for real now. - ACPI bus check notifications for PCI host bridges don't cause the bus below the host bridge to be checked for changes as they should because of a mistake in the ACPI-based PCI hotplug (ACPIPHP) subsystem that forgets to add hotplug contexts to PCI host bridge ACPI device objects. Create hotplug contexts for PCI host bridges too as appropriate. - Revert recent cpufreq commit related to the big.LITTLE cpufreq driver that breaks arm64 builds. - Fix for a regression in the ppc-corenet cpufreq driver introduced during the 3.15 cycle and causing the driver to use the remainder from do_div instead of the quotient. From Ed Swarthout. - Resets triggered by panic activate a BUG_ON() in vmalloc.c on systems where the ACPI reset register is located in memory address space. Fix from Randy Wright. - Fix for a problem with cpufreq governors that decisions made by them may be suboptimal due to the fact that deferrable timers are used by them for CPU load sampling. From Srivatsa S Bhat. - Fix for a problem with the Tegra cpufreq driver where the CPU frequency is temporarily switched to a "stable" level that is different from both the initial and target frequencies during transitions which causes udelay() to expire earlier than it should sometimes. From Viresh Kumar. - New trace points and rework of some existing trace points for system suspend/resume profiling from Todd Brandt. - Assorted cpufreq fixes and cleanups from Stratos Karafotis and Viresh Kumar. - Copyright notice update for suspend-and-cpuhotplug.txt from Srivatsa S Bhat" * tag 'pm+acpi-3.16-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: ACPI / hotplug / PCI: Add hotplug contexts to PCI host bridges PM / sleep: trace events for device PM callbacks cpufreq: cpufreq-cpu0: remove dependency on THERMAL and REGULATOR cpufreq: tegra: update comment for clarity cpufreq: intel_pstate: Remove duplicate CPU ID check cpufreq: Mark CPU0 driver with CPUFREQ_NEED_INITIAL_FREQ_CHECK flag PM / Documentation: Update copyright in suspend-and-cpuhotplug.txt cpufreq: governor: remove copy_prev_load from 'struct cpu_dbs_common_info' cpufreq: governor: Be friendly towards latency-sensitive bursty workloads PM / sleep: trace events for suspend/resume cpufreq: ppc-corenet-cpu-freq: do_div use quotient Revert "cpufreq: Enable big.LITTLE cpufreq driver on arm64" cpufreq: Tegra: implement intermediate frequency callbacks cpufreq: add support for intermediate (stable) frequencies ACPI / video: Change the default for video.use_native_backlight to 1 ACPI: Fix bug when ACPI reset register is implemented in system memory

Merge branch 'pm-sleep'

2014-06-12T11:43:08Z

* pm-sleep: PM / sleep: trace events for device PM callbacks PM / sleep: trace events for suspend/resume

PM / sleep: trace events for suspend/resume

2014-06-06T22:18:07Z

Adds trace events that give finer resolution into suspend/resume. These events are graphed in the timelines generated by the analyze_suspend.py script. They represent large areas of time consumed that are typical to suspend and resume. The event is triggered by calling the function "trace_suspend_resume" with three arguments: a string (the name of the event to be displayed in the timeline), an integer (case specific number, such as the power state or cpu number), and a boolean (where true is used to denote the start of the timeline event, and false to denote the end). The suspend_resume trace event reproduces the data that the machine_suspend trace event did, so the latter has been removed. Signed-off-by: Todd Brandt Acked-by: Steven Rostedt Signed-off-by: Rafael J. Wysocki

kernel/cpu.c: convert printk to pr_foo()

2014-06-04T23:54:14Z

no level printk converted to pr_warn (if err) no level printk converted to pr_info (disabling non-boot cpus) Other printk converted to respective level. Signed-off-by: Fabian Frederick Cc: "Rafael J. Wysocki" Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

sched: Fix hotplug vs. set_cpus_allowed_ptr()

2014-05-22T08:21:31Z

Lai found that: WARNING: CPU: 1 PID: 13 at arch/x86/kernel/smp.c:124 native_smp_send_reschedule+0x2d/0x4b() ... migration_cpu_stop+0x1d/0x22 was caused by set_cpus_allowed_ptr() assuming that cpu_active_mask is always a sub-set of cpu_online_mask. This isn't true since 5fbd036b552f ("sched: Cleanup cpu_active madness"). So set active and online at the same time to avoid this particular problem. Fixes: 5fbd036b552f ("sched: Cleanup cpu_active madness") Signed-off-by: Lai Jiangshan Signed-off-by: Peter Zijlstra Cc: Andrew Morton Cc: Gautham R. Shenoy Cc: Linus Torvalds Cc: Michael wang Cc: Paul Gortmaker Cc: Rafael J. Wysocki Cc: Srivatsa S. Bhat Cc: Toshi Kani Link: http://lkml.kernel.org/r/53758B12.8060609@cn.fujitsu.com Signed-off-by: Ingo Molnar

CPU hotplug: Provide lockless versions of callback registration functions

2014-03-20T12:43:40Z

The following method of CPU hotplug callback registration is not safe due to the possibility of an ABBA deadlock involving the cpu_add_remove_lock and the cpu_hotplug.lock. get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); The deadlock is shown below: CPU 0 CPU 1 ----- ----- Acquire cpu_hotplug.lock [via get_online_cpus()] CPU online/offline operation takes cpu_add_remove_lock [via cpu_maps_update_begin()] Try to acquire cpu_add_remove_lock [via register_cpu_notifier()] CPU online/offline operation tries to acquire cpu_hotplug.lock [via cpu_hotplug_begin()] *** DEADLOCK! *** The problem here is that callback registration takes the locks in one order whereas the CPU hotplug operations take the same locks in the opposite order. To avoid this issue and to provide a race-free method to register CPU hotplug callbacks (along with initialization of already online CPUs), introduce new variants of the callback registration APIs that simply register the callbacks without holding the cpu_add_remove_lock during the registration. That way, we can avoid the ABBA scenario. However, we will need to hold the cpu_add_remove_lock throughout the entire critical section, to protect updates to the callback/notifier chain. This can be achieved by writing the callback registration code as follows: cpu_maps_update_begin(); [ or cpu_notifier_register_begin(); see below ] for_each_online_cpu(cpu) init_cpu(cpu); /* This doesn't take the cpu_add_remove_lock */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_maps_update_done(); [ or cpu_notifier_register_done(); see below ] Note that we can't use get_online_cpus() here instead of cpu_maps_update_begin() because the cpu_hotplug.lock is dropped during the invocation of CPU_POST_DEAD notifiers, and hence get_online_cpus() cannot provide the necessary synchronization to protect the callback/notifier chains against concurrent reads and writes. On the other hand, since the cpu_add_remove_lock protects the entire hotplug operation (including CPU_POST_DEAD), we can use cpu_maps_update_begin/done() to guarantee proper synchronization. Also, since cpu_maps_update_begin/done() is like a super-set of get/put_online_cpus(), the former naturally protects the critical sections from concurrent hotplug operations. Since the names cpu_maps_update_begin/done() don't make much sense in CPU hotplug callback registration scenarios, we'll introduce new APIs named cpu_notifier_register_begin/done() and map them to cpu_maps_update_begin/done(). In summary, introduce the lockless variants of un/register_cpu_notifier() and also export the cpu_notifier_register_begin/done() APIs for use by modules. This way, we provide a race-free way to register hotplug callbacks as well as perform initialization for the CPUs that are already online. Cc: Thomas Gleixner Cc: Andrew Morton Cc: Peter Zijlstra Cc: Ingo Molnar Acked-by: Oleg Nesterov Acked-by: Toshi Kani Reviewed-by: Gautham R. Shenoy Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki

CPU hotplug: Add lockdep annotations to get/put_online_cpus()

2014-03-20T12:43:40Z

Add lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin()/cpu_hotplug_end(). Cc: Ingo Molnar Reviewed-by: Oleg Nesterov Signed-off-by: Gautham R. Shenoy Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki