path: root/kernel/rcu/tree.c
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2016-04-21Merge branches 'doc.2016.04.19a', 'exp.2016.03.31d', 'fixes.2016.03.31d' and ↵Paul E. McKenney-87/+211
'torture.2016.04.21a' into HEAD doc.2016.04.19a: Documentation updates exp.2016.03.31d: Expedited grace-period updates fixes.2016.03.31d: Miscellaneous fixes torture.2016.004.21a Torture-test updates
2016-03-31rcutorture: Expedited-GP batch progress access to torturingPaul E. McKenney-0/+22
This commit provides rcu_exp_batches_completed() and rcu_exp_batches_completed_sched() functions to allow torture-test modules to check how many expedited grace period batches have completed. These are analogous to the existing rcu_batches_completed(), rcu_batches_completed_bh(), and rcu_batches_completed_sched() functions. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Dump ftrace buffer when kicking grace-period kthreadPaul E. McKenney-0/+1
If it is necessary to kick the grace-period kthread, that is a good time to dump the trace buffer in order to learn why kicking was needed. This commit therefore does the dump. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Awaken grace-period kthread if too long since FQSPaul E. McKenney-2/+37
Recent kernels can fail to awaken the grace-period kthread for quiescent-state forcing. This commit is a crude hack that does a wakeup if a scheduling-clock interrupt sees that it has been too long since force-quiescent-state (FQS) processing. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Make FQS schedule advance only if FQS happenedPaul E. McKenney-8/+15
Currently, the force-quiescent-state (FQS) code in rcu_gp_kthread() can advance the next FQS even if one was not executed last time. This can happen due timeout-duration uncertainty. This commit therefore avoids advancing the FQS schedule unless an FQS was just executed. In the corner case where an FQS was not executed, but is due now, the code does a one-jiffy wait. This change prepares for kthread kicking. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Awaken grace-period kthread when stalledPaul E. McKenney-1/+3
Recent kernels can fail to awaken the grace-period kthread for quiescent-state forcing. This commit is a crude hack that does a wakeup any time a stall is detected. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Overlap wakeups with next expedited grace periodPaul E. McKenney-3/+14
The current expedited grace-period implementation makes subsequent grace periods wait on wakeups for the prior grace period. This does not fit the dictionary definition of "expedited", so this commit allows these two phases to overlap. Doing this requires four waitqueues rather than two because tasks can now be waiting on the previous, current, and next grace periods. The fourth waitqueue makes the bit masking work out nicely. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Consolidate expedited GP code into exp_funnel_lock()Paul E. McKenney-3/+2
This commit pulls the grace-period-start counter adjustment and tracing from synchronize_rcu_expedited() and synchronize_sched_expedited() into exp_funnel_lock(), thus eliminating some code duplication. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Consolidate expedited GP tracing into rcu_exp_gp_seq_snap()Paul E. McKenney-3/+5
This commit moves some duplicate code from synchronize_rcu_expedited() and synchronize_sched_expedited() into rcu_exp_gp_seq_snap(). This doesn't save lines of code, but does eliminate a "tell me twice" issue. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Consolidate expedited GP code into rcu_exp_wait_wake()Paul E. McKenney-9/+9
Currently, synchronize_rcu_expedited() and rcu_sched_expedited() have significant duplicate code. This commit therefore consolidates some of this code into rcu_exp_wake(), which is now renamed to rcu_exp_wait_wake() in recognition of its added responsibilities. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Add exp_funnel_lock() fastpathPaul E. McKenney-0/+10
This commit speeds up the low-contention case, especially for systems with large rcu_node trees, by attempting to directly acquire the ->exp_mutex. This fastpath checks the leaves and root first in order to avoid excessive memory contention on the mutex itself. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Enforce expedited-GP fairness via funnel wait queuePaul E. McKenney-74/+81
The current mutex-based funnel-locking approach used by expedited grace periods is subject to severe unfairness. The problem arises when a few tasks, making a path from leaves to root, all wake up before other tasks do. A new task can then follow this path all the way to the root, which needlessly delays tasks whose grace period is done, but who do not happen to acquire the lock quickly enough. This commit avoids this problem by maintaining per-rcu_node wait queues, along with a per-rcu_node counter that tracks the latest grace period sought by an earlier task to visit this node. If that grace period would satisfy the current task, instead of proceeding up the tree, it waits on the current rcu_node structure using a pair of wait queues provided for that purpose. This decouples awakening of old tasks from the arrival of new tasks. If the wakeups prove to be a bottleneck, additional kthreads can be brought to bear for that purpose. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Shorten expedited_workdone* to exp_workdone*Paul E. McKenney-5/+3
Just a name change to save a few lines and a bit of typing. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Force boolean subscript for expedited stall warningsPaul E. McKenney-1/+1
The cpu_online() function can return values other than 0 and 1, which can result in subscript overflow when applied to a two-element array. This commit allows for this behavior by using "!!" on the return value from cpu_online() when used as a subscript. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Remove expedited GP funnel-lock bypassPaul E. McKenney-19/+0
Commit #cdacbe1f91264 ("rcu: Add fastpath bypassing funnel locking") turns out to be a pessimization at high load because it forces a tree full of tasks to wait for an expedited grace period that they probably do not need. This commit therefore removes this optimization. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Add expedited-grace-period event tracingPaul E. McKenney-7/+13
Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Add funnel-locking tracing for expedited grace periodsPaul E. McKenney-4/+27
Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Make cond_resched_rcu_qs() supply RCU-sched expedited QSPaul E. McKenney-0/+15
Although cond_resched_rcu_qs() supplies quiescent states to all flavors of normal RCU grace periods, it does nothing for expedited RCU-sched grace periods. This commit therefore adds a check for a need for a quiescent state from the current CPU by an expedited RCU-sched grace period, and invokes rcu_sched_qs() to supply that quiescent state if so. Note that the check is racy in that we might be migrated to some other CPU just after checking the per-CPU variable. This is OK because the act of migration will do a context switch, which will supply the needed quiescent state. The only downside is that we might do an unnecessary call to rcu_sched_qs(), but the probability is low and the overhead is small. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Make expedited RCU-preempt stall warnings count accuratelyPaul E. McKenney-2/+2
Currently, synchronize_sched_expedited_wait() simply sets the ndetected variable to the rcu_print_task_exp_stall() return value. This means that if the last rcu_node structure has no stalled tasks, record of any stalled tasks in previous rcu_node structures is lost, which can in turn result in failure to dump out the blocking rcu_node structures. Or could, had the test been correct. This commit therefore adds the return value of rcu_print_task_exp_stall() to ndetected and corrects the later test for ndetected. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Make expedited RCU-sched grace period immediately detect idlePaul E. McKenney-0/+5
Currently, sync_sched_exp_handler() will force a reschedule unless this CPU has already checked in or unless a reschedule has already been called for. This is clearly wasteful if sync_sched_exp_handler() interrupted an idle CPU, so this commit immediately reports the quiescent state in that case. Signed-off-by: Paul E. McKenney <>
2016-03-31rcu: Consolidate dumping of ftrace bufferPaul E. McKenney-2/+2
This commit consolidates a couple definitions and several calls for single-shot ftrace-buffer dumping. Signed-off-by: Paul E. McKenney <>
2016-03-15Merge branch 'smp-hotplug-for-linus' of ↵Linus Torvalds-33/+40
git:// Pull cpu hotplug updates from Thomas Gleixner: "This is the first part of the ongoing cpu hotplug rework: - Initial implementation of the state machine - Runs all online and prepare down callbacks on the plugged cpu and not on some random processor - Replaces busy loop waiting with completions - Adds tracepoints so the states can be followed" More detailed commentary on this work from an earlier email: "What's wrong with the current cpu hotplug infrastructure? - Asymmetry The hotplug notifier mechanism is asymmetric versus the bringup and teardown. This is mostly caused by the notifier mechanism. - Largely undocumented dependencies While some notifiers use explicitely defined notifier priorities, we have quite some notifiers which use numerical priorities to express dependencies without any documentation why. - Control processor driven Most of the bringup/teardown of a cpu is driven by a control processor. While it is understandable, that preperatory steps, like idle thread creation, memory allocation for and initialization of essential facilities needs to be done before a cpu can boot, there is no reason why everything else must run on a control processor. Before this patch series, bringup looks like this: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring the rest up - All or nothing approach There is no way to do partial bringups. That's something which is really desired because we waste e.g. at boot substantial amount of time just busy waiting that the cpu comes to life. That's stupid as we could very well do preparatory steps and the initial IPI for other cpus and then go back and do the necessary low level synchronization with the freshly booted cpu. - Minimal debuggability Due to the notifier based design, it's impossible to switch between two stages of the bringup/teardown back and forth in order to test the correctness. So in many hotplug notifiers the cancel mechanisms are either not existant or completely untested. - Notifier [un]registering is tedious To [un]register notifiers we need to protect against hotplug at every callsite. There is no mechanism that bringup/teardown callbacks are issued on the online cpus, so every caller needs to do it itself. That also includes error rollback. What's the new design? The base of the new design is a symmetric state machine, where both the control processor and the booting/dying cpu execute a well defined set of states. Each state is symmetric in the end, except for some well defined exceptions, and the bringup/teardown can be stopped and reversed at almost all states. So the bringup of a cpu will look like this in the future: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu bring itself up The synchronization step does not require the control cpu to wait. That mechanism can be done asynchronously via a worker or some other mechanism. The teardown can be made very similar, so that the dying cpu cleans up and brings itself down. Cleanups which need to be done after the cpu is gone, can be scheduled asynchronously as well. There is a long way to this, as we need to refactor the notion when a cpu is available. Today we set the cpu online right after it comes out of the low level bringup, which is not really correct. The proper mechanism is to set it to available, i.e. cpu local threads, like softirqd, hotplug thread etc. can be scheduled on that cpu, and once it finished all booting steps, it's set to online, so general workloads can be scheduled on it. The reverse happens on teardown. First thing to do is to forbid scheduling of general workloads, then teardown all the per cpu resources and finally shut it off completely. This patch series implements the basic infrastructure for this at the core level. This includes the following: - Basic state machine implementation with well defined states, so ordering and prioritization can be expressed. - Interfaces to [un]register state callbacks This invokes the bringup/teardown callback on all online cpus with the proper protection in place and [un]installs the callbacks in the state machine array. For callbacks which have no particular ordering requirement we have a dynamic state space, so that drivers don't have to register an explicit hotplug state. If a callback fails, the code automatically does a rollback to the previous state. - Sysfs interface to drive the state machine to a particular step. This is only partially functional today. Full functionality and therefor testability will be achieved once we converted all existing hotplug notifiers over to the new scheme. - Run all CPU_ONLINE/DOWN_PREPARE notifiers on the booting/dying processor: Control CPU Booting CPU do preparatory steps kick cpu into life do low level init sync with booting cpu sync with control cpu wait for boot bring itself up Signal completion to control cpu In a previous step of this work we've done a full tree mechanical conversion of all hotplug notifiers to the new scheme. The balance is a net removal of about 4000 lines of code. This is not included in this series, as we decided to take a different approach. Instead of mechanically converting everything over, we will do a proper overhaul of the usage sites one by one so they nicely fit into the symmetric callback scheme. I decided to do that after I looked at the ugliness of some of the converted sites and figured out that their hotplug mechanism is completely buggered anyway. So there is no point to do a mechanical conversion first as we need to go through the usage sites one by one again in order to achieve a full symmetric and testable behaviour" * 'smp-hotplug-for-linus' of git:// (23 commits) cpu/hotplug: Document states better cpu/hotplug: Fix smpboot thread ordering cpu/hotplug: Remove redundant state check cpu/hotplug: Plug death reporting race rcu: Make CPU_DYING_IDLE an explicit call cpu/hotplug: Make wait for dead cpu completion based cpu/hotplug: Let upcoming cpu bring itself fully up arch/hotplug: Call into idle with a proper state cpu/hotplug: Move online calls to hotplugged cpu cpu/hotplug: Create hotplug threads cpu/hotplug: Split out the state walk into functions cpu/hotplug: Unpark smpboot threads from the state machine cpu/hotplug: Move scheduler cpu_online notifier to hotplug core cpu/hotplug: Implement setup/removal interface cpu/hotplug: Make target state writeable cpu/hotplug: Add sysfs state interface cpu/hotplug: Hand in target state to _cpu_up/down cpu/hotplug: Convert the hotplugged cpu work to a state machine cpu/hotplug: Convert to a state machine for the control processor cpu/hotplug: Add tracepoints ...
2016-03-15Merge commit 'fixes.2015.02.23a' into core/rcuIngo Molnar-73/+70
Conflicts: kernel/rcu/tree.c Signed-off-by: Ingo Molnar <>
2016-03-01rcu: Make CPU_DYING_IDLE an explicit callThomas Gleixner-33/+37
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: 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: Signed-off-by: Thomas Gleixner <>
2016-02-25rcu: Use simple wait queues where possible in rcutreePaul Gortmaker-11/+11
As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads GP waits") the RCU subsystem started making use of wait queues. Here we convert all additions of RCU wait queues to use simple wait queues, since they don't need the extra overhead of the full wait queue features. Originally this was done for RT kernels[1], since we would get things like... BUG: sleeping function called from invalid context at kernel/rtmutex.c:659 in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt Pid: 8, comm: rcu_preempt Not tainted Call Trace: [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0 [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50 [<ffffffff8106fcf6>] __wake_up+0x36/0x70 [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680 [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50 [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80 [<ffffffff8105eabb>] kthread+0xdb/0xe0 [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100 [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10 [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60 [<ffffffff817e0750>] ? gs_change+0xb/0xb ...and hence simple wait queues were deployed on RT out of necessity (as simple wait uses a raw lock), but mainline might as well take advantage of the more streamline support as well. [1] This is a carry forward of work from v3.10-rt; the original conversion was by Thomas on an earlier -rt version, and Sebastian extended it to additional post-3.10 added RCU waiters; here I've added a commit log and unified the RCU changes into one, and uprev'd it to match mainline RCU. Signed-off-by: Daniel Wagner <> Acked-by: Peter Zijlstra (Intel) <> Cc: Cc: Boqun Feng <> Cc: Marcelo Tosatti <> Cc: Steven Rostedt <> Cc: Paul Gortmaker <> Cc: Paolo Bonzini <> Cc: "Paul E. McKenney" <> Link: Signed-off-by: Thomas Gleixner <>
2016-02-25rcu: Do not call rcu_nocb_gp_cleanup() while holding rnp->lockDaniel Wagner-1/+3
rcu_nocb_gp_cleanup() is called while holding rnp->lock. Currently, this is okay because the wake_up_all() in rcu_nocb_gp_cleanup() will not enable the IRQs. lockdep is happy. By switching over using swait this is not true anymore. swake_up_all() enables the IRQs while processing the waiters. __do_softirq() can now run and will eventually call rcu_process_callbacks() which wants to grap nrp->lock. Let's move the rcu_nocb_gp_cleanup() call outside the lock before we switch over to swait. If we would hold the rnp->lock and use swait, lockdep reports following: ================================= [ INFO: inconsistent lock state ] 4.2.0-rc5-00025-g9a73ba0 #136 Not tainted --------------------------------- inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. rcu_preempt/8 [HC0[0]:SC0[0]:HE1:SE1] takes: (rcu_node_1){+.?...}, at: [<ffffffff811387c7>] rcu_gp_kthread+0xb97/0xeb0 {IN-SOFTIRQ-W} state was registered at: [<ffffffff81109b9f>] __lock_acquire+0xd5f/0x21e0 [<ffffffff8110be0f>] lock_acquire+0xdf/0x2b0 [<ffffffff81841cc9>] _raw_spin_lock_irqsave+0x59/0xa0 [<ffffffff81136991>] rcu_process_callbacks+0x141/0x3c0 [<ffffffff810b1a9d>] __do_softirq+0x14d/0x670 [<ffffffff810b2214>] irq_exit+0x104/0x110 [<ffffffff81844e96>] smp_apic_timer_interrupt+0x46/0x60 [<ffffffff81842e70>] apic_timer_interrupt+0x70/0x80 [<ffffffff810dba66>] rq_attach_root+0xa6/0x100 [<ffffffff810dbc2d>] cpu_attach_domain+0x16d/0x650 [<ffffffff810e4b42>] build_sched_domains+0x942/0xb00 [<ffffffff821777c2>] sched_init_smp+0x509/0x5c1 [<ffffffff821551e3>] kernel_init_freeable+0x172/0x28f [<ffffffff8182cdce>] kernel_init+0xe/0xe0 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 irq event stamp: 76 hardirqs last enabled at (75): [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 hardirqs last disabled at (76): [<ffffffff8184116f>] _raw_spin_lock_irq+0x1f/0x90 softirqs last enabled at (0): [<ffffffff810a8df2>] copy_process.part.26+0x602/0x1cf0 softirqs last disabled at (0): [< (null)>] (null) other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_1); <Interrupt> lock(rcu_node_1); *** DEADLOCK *** 1 lock held by rcu_preempt/8: #0: (rcu_node_1){+.?...}, at: [<ffffffff811387c7>] rcu_gp_kthread+0xb97/0xeb0 stack backtrace: CPU: 0 PID: 8 Comm: rcu_preempt Not tainted 4.2.0-rc5-00025-g9a73ba0 #136 Hardware name: Dell Inc. PowerEdge R820/066N7P, BIOS 2.0.20 01/16/2014 0000000000000000 000000006d7e67d8 ffff881fb081fbd8 ffffffff818379e0 0000000000000000 ffff881fb0812a00 ffff881fb081fc38 ffffffff8110813b 0000000000000000 0000000000000001 ffff881f00000001 ffffffff8102fa4f Call Trace: [<ffffffff818379e0>] dump_stack+0x4f/0x7b [<ffffffff8110813b>] print_usage_bug+0x1db/0x1e0 [<ffffffff8102fa4f>] ? save_stack_trace+0x2f/0x50 [<ffffffff811087ad>] mark_lock+0x66d/0x6e0 [<ffffffff81107790>] ? check_usage_forwards+0x150/0x150 [<ffffffff81108898>] mark_held_locks+0x78/0xa0 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff81108a28>] trace_hardirqs_on_caller+0x168/0x220 [<ffffffff81108aed>] trace_hardirqs_on+0xd/0x10 [<ffffffff81841330>] _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810fd1c7>] swake_up_all+0xb7/0xe0 [<ffffffff811386e1>] rcu_gp_kthread+0xab1/0xeb0 [<ffffffff811089bf>] ? trace_hardirqs_on_caller+0xff/0x220 [<ffffffff81841341>] ? _raw_spin_unlock_irq+0x41/0x60 [<ffffffff81137c30>] ? rcu_barrier+0x20/0x20 [<ffffffff810d2014>] kthread+0x104/0x120 [<ffffffff81841330>] ? _raw_spin_unlock_irq+0x30/0x60 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 [<ffffffff8184231f>] ret_from_fork+0x3f/0x70 [<ffffffff810d1f10>] ? kthread_create_on_node+0x260/0x260 Signed-off-by: Daniel Wagner <> Acked-by: Peter Zijlstra (Intel) <> Cc: Cc: Boqun Feng <> Cc: Marcelo Tosatti <> Cc: Steven Rostedt <> Cc: Paul Gortmaker <> Cc: Paolo Bonzini <> Cc: "Paul E. McKenney" <> Link: Signed-off-by: Thomas Gleixner <>
2016-02-23rcu: Catch up rcu_report_qs_rdp() comment with realityPaul E. McKenney-6/+1
Signed-off-by: Paul E. McKenney <>
2016-02-23RCU: Privatize rcu_node::lockBoqun Feng-51/+52
In patch: "rcu: Add transitivity to remaining rcu_node ->lock acquisitions" All locking operations on rcu_node::lock are replaced with the wrappers because of the need of transitivity, which indicates we should never write code using LOCK primitives alone(i.e. without a proper barrier following) on rcu_node::lock outside those wrappers. We could detect this kind of misuses on rcu_node::lock in the future by adding __private modifier on rcu_node::lock. To privatize rcu_node::lock, unlock wrappers are also needed. Replacing spinlock unlocks with these wrappers not only privatizes rcu_node::lock but also makes it easier to figure out critical sections of rcu_node. This patch adds __private modifier to rcu_node::lock and makes every access to it wrapped by ACCESS_PRIVATE(). Besides, unlock wrappers are added and raw_spin_unlock(&rnp->lock) and its friends are replaced with those wrappers. Signed-off-by: Boqun Feng <> Signed-off-by: Paul E. McKenney <>
2016-02-23rcu: Remove useless rcu_data_p when !PREEMPT_RCUChen Gang-1/+0
The related warning from gcc 6.0: In file included from kernel/rcu/tree.c:4630:0: kernel/rcu/tree_plugin.h:810:40: warning: ‘rcu_data_p’ defined but not used [-Wunused-const-variable] static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data; ^~~~~~~~~~ Also remove always redundant rcu_data_p in tree.c. Signed-off-by: Chen Gang <> Signed-off-by: Paul E. McKenney <>
2016-02-23rcu: Set rdp->gpwrap when CPU is idlePaul E. McKenney-3/+2
Commit #e3663b1024d1 ("rcu: Handle gpnum/completed wrap while dyntick idle") sets rdp->gpwrap on the wrong side of the "if" statement in dyntick_save_progress_counter(), that is, it sets it when the CPU is not idle instead of when it is idle. Of course, if the CPU is not idle, its rdp->gpnum won't be lagging beind the global rsp->gpnum, which means that rdp->gpwrap will never be set. This commit therefore moves this code to the proper leg of that "if" statement. This change means that the "else" cause is just "return 0" and the "then" clause ends with "return 1", so also move the "return 0" to follow the "if", dropping the "else" clause. Signed-off-by: Paul E. McKenney <>
2016-02-23rcu: Stop treating in-kernel CPU-bound workloads as errorsPaul E. McKenney-6/+7
Commit 4a81e8328d379 ("Reduce overhead of cond_resched() checks for RCU") handles the error case where a nohz_full loops indefinitely in the kernel with the scheduling-clock interrupt disabled. However, this handling includes IPIing the CPU running the offending loop, which is not what we want for real-time workloads. And there are starting to be real-time CPU-bound in-kernel workloads, and these must be handled without IPIing the CPU, at least not in the common case. Therefore, this situation can no longer be dismissed as an error case. This commit therefore splits the handling out, so that the setting of bits in the per-CPU rcu_sched_qs_mask variable is done relatively early, but if the problem persists, resched_cpu() is eventually used to IPI the CPU containing the offending loop. Assuming that in-kernel CPU-bound loops used by real-time tasks contain frequent calls cond_resched_rcu_qs() (as in more than once per few tens of milliseconds), the real-time tasks will never be IPIed. Signed-off-by: Paul E. McKenney <> Cc: Steven Rostedt <>
2016-02-23rcu: Update rcu_report_qs_rsp() commentPaul E. McKenney-5/+7
The header comment for rcu_report_qs_rsp() was obsolete, dating well before the advent of RCU grace-period kthreads. This commit therefore brings this comment back into alignment with current reality. Reported-by: Lihao Liang <> Signed-off-by: Paul E. McKenney <>
2016-02-23rcu: Assign false instead of 0 for ->core_needs_qsPaul E. McKenney-1/+1
A zero seems to have escaped earlier true/false substitution efforts, so this commit changes 0 to false for the ->core_needs_qs boolean field. Signed-off-by: Paul E. McKenney <>
2015-12-07Merge branches 'doc.2015.12.05a', 'exp.2015.12.07a', 'fixes.2015.12.07a', ↵Paul E. McKenney-82/+135
'list.2015.12.04b' and 'torture.2015.12.05a' into HEAD doc.2015.12.05a: Documentation updates exp.2015.12.07a: Expedited grace-period updates fixes.2015.12.07a: Miscellaneous fixes list.2015.12.04b: Linked-list updates torture.2015.12.05a: Torture-test updates
2015-12-07rcu: Make rcu_gp_init() be bool rather than intPaul E. McKenney-5/+5
The return value from rcu_gp_init() is always used as a bool, so this commit makes it be a bool. Reported-by: Iftekhar Ahmed <> Signed-off-by: Paul E. McKenney <>
2015-12-07rcu: Move wakeup out from under rnp->lockPeter Zijlstra-1/+1
This patch removes a potential deadlock hazard by moving the wake_up_process() in rcu_spawn_gp_kthread() out from under rnp->lock. Signed-off-by: Peter Zijlstra <> Signed-off-by: Paul E. McKenney <>
2015-12-07rcu: Don't redundantly disable irqs in rcu_irq_{enter,exit}()Paul E. McKenney-6/+26
This commit replaces a local_irq_save()/local_irq_restore() pair with a lockdep assertion that interrupts are already disabled. This should remove the corresponding overhead from the interrupt entry/exit fastpaths. This change was inspired by the fact that Iftekhar Ahmed's mutation testing showed that removing rcu_irq_enter()'s call to local_ird_restore() had no effect, which might indicate that interrupts were always enabled anyway. Signed-off-by: Paul E. McKenney <>
2015-12-07rcu: Make cpu_needs_another_gp() be boolPaul E. McKenney-7/+7
The cpu_needs_another_gp() function is currently of type int, but only returns zero or one. Bow to reality and make it be of type bool. Signed-off-by: Paul E. McKenney <>
2015-12-07rcu: Eliminate unused rcu_init_one() argumentPaul E. McKenney-4/+3
Now that the rcu_state structure's ->rda field is compile-time initialized, there is no need to pass the per-CPU rcu_data structure into rcu_init_one(). This commit therefore eliminates this now-unused parameter. Signed-off-by: Paul E. McKenney <>
2015-12-05rcutorture: Print symbolic name for ->gp_statePaul E. McKenney-2/+13
Currently, ->gp_state is printed as an integer, which slows debugging. This commit therefore prints a symbolic name in addition to the integer. Signed-off-by: Paul E. McKenney <> [ paulmck: Updated to fix relational operator called out by Dan Carpenter. ] [ paulmck: More "const", as suggested by Josh Triplett. ] Reviewed-by: Josh Triplett <>
2015-12-05rcutorture: Dump stack when GP kthread stallsPaul E. McKenney-1/+4
This commit increases debug information in the case where the grace-period kthread is being prevented from running by dumping that kthread's stack. Signed-off-by: Paul E. McKenney <> [ paulmck: Split into prior commit and this commit, as suggested by Josh Triplett. ] Reviewed-by: Josh Triplett <>
2015-12-05rcutorture: Flag nonexistent RCU GP kthreadPaul E. McKenney-1/+1
Currently, if the RCU grace-period kthread has not yet been created, in which case the starvation-check code will print zero for the state, which maps to TASK_RUNNING. This could clearly be quite confusing, so this commit prints ~0, which does not map to any legal ->state value. Signed-off-by: Paul E. McKenney <> Reviewed-by: Josh Triplett <>
2015-12-04rcu: Stop disabling interrupts in scheduler fastpathsPaul E. McKenney-15/+12
We need the scheduler's fastpaths to be, well, fast, and unnecessarily disabling and re-enabling interrupts is not necessarily consistent with this goal. Especially given that there are regions of the scheduler that already have interrupts disabled. This commit therefore moves the call to rcu_note_context_switch() to one of the interrupts-disabled regions of the scheduler, and removes the now-redundant disabling and re-enabling of interrupts from rcu_note_context_switch() and the functions it calls. Reported-by: Peter Zijlstra <> Signed-off-by: Paul E. McKenney <> [ paulmck: Shift rcu_note_context_switch() to avoid deadlock, as suggested by Peter Zijlstra. ]
2015-12-04rcu: Simplify rcu_sched_qs() control flowPaul E. McKenney-15/+14
This commit applies an early-exit approach to rcu_sched_qs(), reducing the nesting level and saving a line of code. Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Move lock_class_key to local scopePaul E. McKenney-4/+3
Currently, the rcu_node_class[], rcu_fqs_class[], and rcu_exp_class[] arrays needlessly pollute the global namespace within tree.c. This commit therefore converts them to static local variables within rcu_init_one(). Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Add rcu_normal kernel parameter to suppress expeditingPaul E. McKenney-0/+6
Although expedited grace periods can be quite useful, and although their OS jitter has been greatly reduced, they can still pose problems for extreme real-time workloads. This commit therefore adds a rcu_normal kernel boot parameter (which can also be manipulated via sysfs) to suppress expedited grace periods, that is, to treat requests for expedited grace periods as if they were requests for normal grace periods. If both rcu_expedited and rcu_normal are specified, rcu_normal wins. This means that if you are relying on expedited grace periods to speed up boot, you will want to specify rcu_expedited on the kernel command line, and then specify rcu_normal via sysfs once boot completes. Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Add more diagnostics to expedited stall warning messages.Paul E. McKenney-3/+21
This commit adds print statements that check the rcu_node structure to find which ->expmask bits and which ->exp_tasks structures are blocking the current expedited grace period. Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Make expedited grace periods resolve stall-warning tiesPaul E. McKenney-1/+1
Currently, if a grace period ends just as the stall-warning timeout fires, an empty stall warning will be printed. This is not helpful, so this commit avoids these useless warnings by rechecking completion after awakening in synchronize_sched_expedited_wait(). Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Reduce expedited GP memory contention via per-CPU variablesPaul E. McKenney-6/+5
Currently, the piggybacked-work checks carried out by sync_exp_work_done() atomically increment a small set of variables (the ->expedited_workdone0, ->expedited_workdone1, ->expedited_workdone2, ->expedited_workdone3 fields in the rcu_state structure), which will form a memory-contention bottleneck given a sufficiently large number of CPUs concurrently invoking either synchronize_rcu_expedited() or synchronize_sched_expedited(). This commit therefore moves these for fields to the per-CPU rcu_data structure, eliminating the memory contention. The show_rcuexp() function also changes to sum up each field in the rcu_data structures. Signed-off-by: Paul E. McKenney <>
2015-12-04rcu: Invert sync_rcu_exp_select_cpus() "if" statementPaul E. McKenney-16/+14
This commit saves a couple lines of code and reduces indentation by inverting the sense of an "if" statement in the function sync_rcu_exp_select_cpus(). Signed-off-by: Paul E. McKenney <>