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* Merge branch 'locking-core-for-linus' of ↵Linus Torvalds2017-11-131-8/+8
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull core locking updates from Ingo Molnar: "The main changes in this cycle are: - Another attempt at enabling cross-release lockdep dependency tracking (automatically part of CONFIG_PROVE_LOCKING=y), this time with better performance and fewer false positives. (Byungchul Park) - Introduce lockdep_assert_irqs_enabled()/disabled() and convert open-coded equivalents to lockdep variants. (Frederic Weisbecker) - Add down_read_killable() and use it in the VFS's iterate_dir() method. (Kirill Tkhai) - Convert remaining uses of ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE(). Most of the conversion was Coccinelle driven. (Mark Rutland, Paul E. McKenney) - Get rid of lockless_dereference(), by strengthening Alpha atomics, strengthening READ_ONCE() with smp_read_barrier_depends() and thus being able to convert users of lockless_dereference() to READ_ONCE(). (Will Deacon) - Various micro-optimizations: - better PV qspinlocks (Waiman Long), - better x86 barriers (Michael S. Tsirkin) - better x86 refcounts (Kees Cook) - ... plus other fixes and enhancements. (Borislav Petkov, Juergen Gross, Miguel Bernal Marin)" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (70 commits) locking/x86: Use LOCK ADD for smp_mb() instead of MFENCE rcu: Use lockdep to assert IRQs are disabled/enabled netpoll: Use lockdep to assert IRQs are disabled/enabled timers/posix-cpu-timers: Use lockdep to assert IRQs are disabled/enabled sched/clock, sched/cputime: Use lockdep to assert IRQs are disabled/enabled irq_work: Use lockdep to assert IRQs are disabled/enabled irq/timings: Use lockdep to assert IRQs are disabled/enabled perf/core: Use lockdep to assert IRQs are disabled/enabled x86: Use lockdep to assert IRQs are disabled/enabled smp/core: Use lockdep to assert IRQs are disabled/enabled timers/hrtimer: Use lockdep to assert IRQs are disabled/enabled timers/nohz: Use lockdep to assert IRQs are disabled/enabled workqueue: Use lockdep to assert IRQs are disabled/enabled irq/softirqs: Use lockdep to assert IRQs are disabled/enabled locking/lockdep: Add IRQs disabled/enabled assertion APIs: lockdep_assert_irqs_enabled()/disabled() locking/pvqspinlock: Implement hybrid PV queued/unfair locks locking/rwlocks: Fix comments x86/paravirt: Set up the virt_spin_lock_key after static keys get initialized block, locking/lockdep: Assign a lock_class per gendisk used for wait_for_completion() workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes ...
| * rcu: Use lockdep to assert IRQs are disabled/enabledFrederic Weisbecker2017-11-081-8/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Lockdep now has an integrated IRQs disabled/enabled sanity check. Just use it instead of the ad-hoc RCU version. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Acked-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: David S . Miller <davem@davemloft.net> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/r/1509980490-4285-15-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* | Merge branch 'for-mingo' of ↵Ingo Molnar2017-10-241-32/+127
|\ \ | |/ |/| | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu Pull RCU updates from Paul E. McKenney: - Documentation updates - Miscellaneous fixes - RCU CPU stall-warning updates - Torture-test updates Signed-off-by: Ingo Molnar <mingo@kernel.org>
| *-. Merge branches 'doc.2017.10.20a', 'fixes.2017.10.19a', 'stall.2017.10.09a' ↵Paul E. McKenney2017-10-201-32/+127
| |\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | and 'torture.2017.10.09a' into HEAD doc.2017.10.20a: Documentation updates. fixes.2017.10.19a: Miscellaneous fixes. stall.2017.10.09a: RCU CPU stall-warning updates. torture.2017.10.09a: Torture-test updates.
| | | * rcu: Make RCU CPU stall warnings check for irq-disabled CPUsPaul E. McKenney2017-10-091-12/+92
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | One common question upon seeing an RCU CPU stall warning is "did the stalled CPUs have interrupts disabled?" However, the current stall warnings are silent on this point. This commit therefore uses irq_work to check whether stalled CPUs still respond to IPIs, and flags this state in the RCU CPU stall warning console messages. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * sched,rcu: Make cond_resched() provide RCU quiescent statePaul E. McKenney2017-10-091-20/+5
| | |/ | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There is some confusion as to which of cond_resched() or cond_resched_rcu_qs() should be added to long in-kernel loops. This commit therefore eliminates the decision by adding RCU quiescent states to cond_resched(). This commit also simplifies the code that used to interact with cond_resched_rcu_qs(), and that now interacts with cond_resched(), to reduce its overhead. This reduction is necessary to allow the heavier-weight cond_resched_rcu_qs() mechanism to be invoked everywhere that cond_resched() is invoked. Part of that reduction in overhead converts the jiffies_till_sched_qs kernel parameter to read-only at runtime, thus eliminating the need for bounds checking. Reported-by: Michal Hocko <mhocko@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> [ paulmck: Keep PREEMPT=n cond_resched a no-op, per Peter Zijlstra. ]
| | * rcu: Add extended-quiescent-state testing advicePaul E. McKenney2017-10-191-0/+30
| |/ | | | | | | | | | | | | | | | | | | If you add or remove calls to rcu_idle_enter(), rcu_user_enter(), rcu_irq_exit(), rcu_irq_exit_irqson(), rcu_idle_exit(), rcu_user_exit(), rcu_irq_enter(), rcu_irq_enter_irqson(), rcu_nmi_enter(), or rcu_nmi_exit(), you should run a full set of tests on a kernel built with CONFIG_RCU_EQS_DEBUG=y. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Fix various RCU docbook comment-header problemsPaul E. McKenney2017-10-191-8/+10
|/ | | | | | | | Because many of RCU's files have not been included into docbook, a number of errors have accumulated. This commit fixes them. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge tag 'trace-v4.14-rc1-3' of ↵Linus Torvalds2017-10-041-2/+2
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing fixlets from Steven Rostedt: "Two updates: - A memory fix with left over code from spliting out ftrace_ops and function graph tracer, where the function graph tracer could reset the trampoline pointer, leaving the old trampoline not to be freed (memory leak). - The update to Paul's patch that added the unnecessary READ_ONCE(). This removes the unnecessary READ_ONCE() instead of having to rebase the branch to update the patch that added it" * tag 'trace-v4.14-rc1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: rcu: Remove extraneous READ_ONCE()s from rcu_irq_{enter,exit}() ftrace: Fix kmemleak in unregister_ftrace_graph
| * rcu: Remove extraneous READ_ONCE()s from rcu_irq_{enter,exit}()Paul E. McKenney2017-10-031-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The read of ->dynticks_nmi_nesting in rcu_irq_enter() and rcu_irq_exit() is currently protected with READ_ONCE(). However, this protection is unnecessary because (1) ->dynticks_nmi_nesting is updated only by the current CPU, (2) Although NMI handlers can update this field, they reset it back to its old value before return, and (3) Interrupts are disabled, so nothing else can modify it. The value of ->dynticks_nmi_nesting is thus effectively constant, and so no protection is required. This commit therefore removes the READ_ONCE() protection from these two accesses. Link: http://lkml.kernel.org/r/20170926031902.GA2074@linux.vnet.ibm.com Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* | Merge tag 'trace-v4.14-rc1-2' of ↵Linus Torvalds2017-09-251-0/+10
|\ \ | |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing fixes from Steven Rostedt: "Stack tracing and RCU has been having issues with each other and lockdep has been pointing out constant problems. The changes have been going into the stack tracer, but it has been discovered that the problem isn't with the stack tracer itself, but it is with calling save_stack_trace() from within the internals of RCU. The stack tracer is the one that can trigger the issue the easiest, but examining the problem further, it could also happen from a WARN() in the wrong place, or even if an NMI happened in this area and it did an rcu_read_lock(). The critical area is where RCU is not watching. Which can happen while going to and from idle, or bringing up or taking down a CPU. The final fix was to put the protection in kernel_text_address() as it is the one that requires RCU to be watching while doing the stack trace. To make this work properly, Paul had to allow rcu_irq_enter() happen after rcu_nmi_enter(). This should have been done anyway, since an NMI can page fault (reading vmalloc area), and a page fault triggers rcu_irq_enter(). One patch is just a consolidation of code so that the fix only needed to be done in one location" * tag 'trace-v4.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: tracing: Remove RCU work arounds from stack tracer extable: Enable RCU if it is not watching in kernel_text_address() extable: Consolidate *kernel_text_address() functions rcu: Allow for page faults in NMI handlers
| * rcu: Allow for page faults in NMI handlersPaul E. McKenney2017-09-231-0/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | A number of architecture invoke rcu_irq_enter() on exception entry in order to allow RCU read-side critical sections in the exception handler when the exception is from an idle or nohz_full CPU. This works, at least unless the exception happens in an NMI handler. In that case, rcu_nmi_enter() would already have exited the extended quiescent state, which would mean that rcu_irq_enter() would (incorrectly) cause RCU to think that it is again in an extended quiescent state. This will in turn result in lockdep splats in response to later RCU read-side critical sections. This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to take no action if there is an rcu_nmi_enter() in effect, thus avoiding the unscheduled return to RCU quiescent state. This in turn should make the kernel safe for on-demand RCU voyeurism. Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com Cc: stable@vger.kernel.org Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
* | treewide: make "nr_cpu_ids" unsignedAlexey Dobriyan2017-09-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | First, number of CPUs can't be negative number. Second, different signnnedness leads to suboptimal code in the following cases: 1) kmalloc(nr_cpu_ids * sizeof(X)); "int" has to be sign extended to size_t. 2) while (loff_t *pos < nr_cpu_ids) MOVSXD is 1 byte longed than the same MOV. Other cases exist as well. Basically compiler is told that nr_cpu_ids can't be negative which can't be deduced if it is "int". Code savings on allyesconfig kernel: -3KB add/remove: 0/0 grow/shrink: 25/264 up/down: 261/-3631 (-3370) function old new delta coretemp_cpu_online 450 512 +62 rcu_init_one 1234 1272 +38 pci_device_probe 374 399 +25 ... pgdat_reclaimable_pages 628 556 -72 select_fallback_rq 446 369 -77 task_numa_find_cpu 1923 1807 -116 Link: http://lkml.kernel.org/r/20170819114959.GA30580@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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*---. \ Merge branches 'doc.2017.08.17a', 'fixes.2017.08.17a', ↵Paul E. McKenney2017-08-171-128/+85
|\ \ \ \ | |_|_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'hotplug.2017.07.25b', 'misc.2017.08.17a', 'spin_unlock_wait_no.2017.08.17a', 'srcu.2017.07.27c' and 'torture.2017.07.24c' into HEAD doc.2017.08.17a: Documentation updates. fixes.2017.08.17a: RCU fixes. hotplug.2017.07.25b: CPU-hotplug updates. misc.2017.08.17a: Miscellaneous fixes outside of RCU (give or take conflicts). spin_unlock_wait_no.2017.08.17a: Remove spin_unlock_wait(). srcu.2017.07.27c: SRCU updates. torture.2017.07.24c: Torture-test updates.
| | | * rcu: Add last-CPU to GP-kthread starvation messagesPaul E. McKenney2017-07-241-2/+3
| |_|/ |/| | | | | | | | | | | | | | | | | This commit augments the grace-period-kthread starvation debugging messages by adding the last CPU that ran the kthread. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Move callback-list warning to irq-disable regionPaul E. McKenney2017-07-251-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | After adopting callbacks from a newly offlined CPU, the adopting CPU checks to make sure that its callback list's count is zero only if the list has no callbacks and vice versa. Unfortunately, it does so after enabling interrupts, which means that false positives are possible due to interrupt handlers invoking call_rcu(). Although these false positives are improbable, rcutorture did make it happen once. This commit therefore moves this check to an irq-disabled region of code, thus suppressing the false positive. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Localize rcu_state ->orphan_pend and ->orphan_donePaul E. McKenney2017-07-251-69/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Given that the rcu_state structure's >orphan_pend and ->orphan_done fields are used only during migration of callbacks from the recently offlined CPU to a surviving CPU, if rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() are combined, these fields can become local variables in the combined function. This commit therefore combines rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() into a new rcu_segcblist_merge() function and removes the ->orphan_pend and ->orphan_done fields. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Advance callbacks after migrationPaul E. McKenney2017-07-251-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | When migrating callbacks from a newly offlined CPU, we are already holding the root rcu_node structure's lock, so it costs almost nothing to advance and accelerate the newly migrated callbacks. This patch therefore makes this advancing and acceleration happen. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Eliminate rcu_state ->orphan_lockPaul E. McKenney2017-07-251-12/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | The ->orphan_lock is acquired and released only within the rcu_migrate_callbacks() function, which now acquires the root rcu_node structure's ->lock. This commit therefore eliminates the ->orphan_lock in favor of the root rcu_node structure's ->lock. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Advance outgoing CPU's callbacks before migrating themPaul E. McKenney2017-07-251-1/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It is possible that the outgoing CPU is unaware of recent grace periods, and so it is also possible that some of its pending callbacks are actually ready to be invoked. The current callback-migration code would needlessly force these callbacks to pass through another grace period. This commit therefore invokes rcu_advance_cbs() on the outgoing CPU's callbacks in order to give them full credit for having passed through any recent grace periods. This also fixes an odd theoretical bug where there are no callbacks in the system except for those on the outgoing CPU, none of those callbacks have yet been associated with a grace-period number, there is never again another callback registered, and the surviving CPU never again takes a scheduling-clock interrupt, never goes idle, and never enters nohz_full userspace execution. Yes, this is (just barely) possible. It requires that the surviving CPU be a nohz_full CPU, that its scheduler-clock interrupt be shut off, and that it loop forever in the kernel. You get bonus points if you can make this one happen! ;-) Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Make NOCB CPUs migrate CBs directly from outgoing CPUPaul E. McKenney2017-07-251-6/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | RCU's CPU-hotplug callback-migration code first moves the outgoing CPU's callbacks to ->orphan_done and ->orphan_pend, and only then moves them to the NOCB callback list. This commit avoids the extra step (and simplifies the code) by moving the callbacks directly from the outgoing CPU's callback list to the NOCB callback list. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Check for NOCB CPUs and empty lists earlier in CB migrationPaul E. McKenney2017-07-251-4/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current CPU-hotplug RCU-callback-migration code checks for the source (newly offlined) CPU being a NOCBs CPU down in rcu_send_cbs_to_orphanage(). This commit simplifies callback migration a bit by moving this check up to rcu_migrate_callbacks(). This commit also adds a check for the source CPU having no callbacks, which eases analysis of the rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() functions. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Remove orphan/adopt event-tracing fieldsPaul E. McKenney2017-07-251-2/+0
| | | | | | | | | | | | | | | | | | | | | The rcu_node structure's ->n_cbs_orphaned and ->n_cbs_adopted fields are updated, but never read. This commit therefore removes them. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Make expedited GPs correctly handle hardware CPU insertionPaul E. McKenney2017-07-251-2/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The update of the ->expmaskinitnext and of ->ncpus are unsynchronized, with the value of ->ncpus being incremented long before the corresponding ->expmaskinitnext mask is updated. If an RCU expedited grace period sees ->ncpus change, it will update the ->expmaskinit masks from the new ->expmaskinitnext masks. But it is possible that ->ncpus has already been updated, but the ->expmaskinitnext masks still have their old values. For the current expedited grace period, no harm done. The CPU could not have been online before the grace period started, so there is no need to wait for its non-existent pre-existing readers. But the next RCU expedited grace period is in a world of hurt. The value of ->ncpus has already been updated, so this grace period will assume that the ->expmaskinitnext masks have not changed. But they have, and they won't be taken into account until the next never-been-online CPU comes online. This means that RCU will be ignoring some CPUs that it should be paying attention to. The solution is to update ->ncpus and ->expmaskinitnext while holding the ->lock for the rcu_node structure containing the ->expmaskinitnext mask. Because smp_store_release() is now used to update ->ncpus and smp_load_acquire() is now used to locklessly read it, if the expedited grace period sees ->ncpus change, then the updating CPU has to already be holding the corresponding ->lock. Therefore, when the expedited grace period later acquires that ->lock, it is guaranteed to see the new value of ->expmaskinitnext. On the other hand, if the expedited grace period loads ->ncpus just before an update, earlier full memory barriers guarantee that the incoming CPU isn't far enough along to be running any RCU readers. This commit therefore makes the required change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Migrate callbacks earlier in the CPU-offline timelinePaul E. McKenney2017-07-251-96/+113
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | RCU callbacks must be migrated away from an outgoing CPU, and this is done near the end of the CPU-hotplug operation, after the outgoing CPU is long gone. Unfortunately, this means that other CPU-hotplug callbacks can execute while the outgoing CPU's callbacks are still immobilized on the long-gone CPU's callback lists. If any of these CPU-hotplug callbacks must wait, either directly or indirectly, for the invocation of any of the immobilized RCU callbacks, the system will hang. This commit avoids such hangs by migrating the callbacks away from the outgoing CPU immediately upon its departure, shortly after the return from __cpu_die() in takedown_cpu(). Thus, RCU is able to advance these callbacks and invoke them, which allows all the after-the-fact CPU-hotplug callbacks to wait on these RCU callbacks without risk of a hang. While in the neighborhood, this commit also moves rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() under a pre-existing #ifdef to avoid including dead code on the one hand and to avoid define-without-use warnings on the other hand. Reported-by: Jeffrey Hugo <jhugo@codeaurora.org> Link: http://lkml.kernel.org/r/db9c91f6-1b17-6136-84f0-03c3c2581ab4@codeaurora.org Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Anna-Maria Gleixner <anna-maria@linutronix.de> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Richard Weinberger <richard@nod.at>
| * rcu: Remove exports from rcu_idle_exit() and rcu_idle_enter()Paul E. McKenney2017-08-171-2/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_idle_exit() and rcu_idle_enter() functions are exported because they were originally used by RCU_NONIDLE(), which was intended to be usable from modules. However, RCU_NONIDLE() now instead uses rcu_irq_enter_irqson() and rcu_irq_exit_irqson(), which are not exported, and there have been no complaints. This commit therefore removes the exports from rcu_idle_exit() and rcu_idle_enter(). Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Add warning to rcu_idle_enter() for irqs enabledPaul E. McKenney2017-08-171-1/+2
| | | | | | | | | | | | | | | | | | All current callers of rcu_idle_enter() have irqs disabled, and rcu_idle_enter() relies on this, but doesn't check. This commit therefore adds a RCU_LOCKDEP_WARN() to add some verification to the trust. While we are there, pass "true" rather than "1" to rcu_eqs_enter(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Make rcu_idle_enter() rely on callers disabling irqsPeter Zijlstra (Intel)2017-08-171-4/+1
| | | | | | | | | | | | | | | | | | All callers to rcu_idle_enter() have irqs disabled, so there is no point in rcu_idle_enter disabling them again. This commit therefore replaces the irq disabling with a RCU_LOCKDEP_WARN(). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Add assertions verifying blocked-tasks listPaul E. McKenney2017-08-171-0/+2
| | | | | | | | | | | | | | | | | | This commit adds assertions verifying the consistency of the rcu_node structure's ->blkd_tasks list and its ->gp_tasks, ->exp_tasks, and ->boost_tasks pointers. In particular, the ->blkd_tasks lists must be empty except for leaf rcu_node structures. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu/tracing: Set disable_rcu_irq_enter on rcu_eqs_exit()Masami Hiramatsu2017-08-171-0/+2
| | | | | | | | | | | | | | | | | | | | | | Set disable_rcu_irq_enter on not only rcu_eqs_enter_common() but also rcu_eqs_exit(), since rcu_eqs_exit() suffers from the same issue as was fixed for rcu_eqs_enter_common() by commit 03ecd3f48e57 ("rcu/tracing: Add rcu_disabled to denote when rcu_irq_enter() will not work"). Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Add TPS() protection for _rcu_barrier_trace stringsPaul E. McKenney2017-08-171-12/+15
| | | | | | | | | | | | | | | | | | | | | | The _rcu_barrier_trace() function is a wrapper for trace_rcu_barrier(), which needs TPS() protection for strings passed through the second argument. However, it has escaped prior TPS()-ification efforts because it _rcu_barrier_trace() does not start with "trace_". This commit therefore adds the needed TPS() protection Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
| * rcu: Use idle versions of swait to make idle-hack clearLuis R. Rodriguez2017-08-171-6/+5
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | These RCU waits were set to use interruptible waits to avoid the kthreads contributing to system load average, even though they are not interruptible as they are spawned from a kthread. Use the new TASK_IDLE swaits which makes our goal clear, and removes confusion about these paths possibly being interruptible -- they are not. When the system is idle the RCU grace-period kthread will spend all its time blocked inside the swait_event_interruptible(). If the interruptible() was not used, then this kthread would contribute to the load average. This means that an idle system would have a load average of 2 (or 3 if PREEMPT=y), rather than the load average of 0 that almost fifty years of UNIX has conditioned sysadmins to expect. The same argument applies to swait_event_interruptible_timeout() use. The RCU grace-period kthread spends its time blocked inside this call while waiting for grace periods to complete. In particular, if there was only one busy CPU, but that CPU was frequently invoking call_rcu(), then the RCU grace-period kthread would spend almost all its time blocked inside the swait_event_interruptible_timeout(). This would mean that the load average would be 2 rather than the expected 1 for the single busy CPU. Acked-by: "Eric W. Biederman" <ebiederm@xmission.com> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove nohz_full full-system-idle state machinePaul E. McKenney2017-06-081-34/+7
| | | | | | | | | | | | | | The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013 by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"), but has not been used. This commit therefore removes it. If it turns out to be needed later, this commit can always be reverted. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
* rcu: Remove the RCU_KTHREAD_PRIO Kconfig optionPaul E. McKenney2017-06-081-4/+0
| | | | | | | | | | | Anything that can be done with the RCU_KTHREAD_PRIO Kconfig option can also be done with the rcutree.kthread_prio kernel boot parameter. This commit therefore removes this Kconfig option. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Rik van Riel <riel@redhat.com>
* rcu: Remove *_SLOW_* Kconfig optionsPaul E. McKenney2017-06-081-20/+6
| | | | | | | | | | | | | | | | | | | | | | The RCU_TORTURE_TEST_SLOW_PREINIT, RCU_TORTURE_TEST_SLOW_PREINIT_DELAY, RCU_TORTURE_TEST_SLOW_PREINIT_DELAY, RCU_TORTURE_TEST_SLOW_INIT, RCU_TORTURE_TEST_SLOW_INIT_DELAY, RCU_TORTURE_TEST_SLOW_CLEANUP, and RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY Kconfig options are only useful for torture testing, and there are the rcutree.gp_cleanup_delay, rcutree.gp_init_delay, and rcutree.gp_preinit_delay kernel boot parameters that rcutorture can use instead. The effect of these parameters is to artificially slow down grace period initialization and cleanup in order to make some types of race conditions happen more often. This commit therefore simplifies Tree RCU a bit by removing the Kconfig options and adding the corresponding kernel parameters to rcutorture's .boot files instead. However, this commit also leaves out the kernel parameters for TREE02, TREE04, and TREE07 in order to have about the same number of tests slowed as not slowed. TREE01, TREE03, TREE05, and TREE06 are slowed, and the rest are not slowed. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Improve __call_rcu() debug-objects error messagePaul E. McKenney2017-06-081-2/+7
| | | | | | | | | | | | The "__call_rcu(): Leaked duplicate callback" error message from __call_rcu() has proven to be unhelpful. This commit therefore changes it to "__call_rcu(): Double-freed CB" and adds the value of the pointer passed in. The value of the pointer improves debuggability by allowing correlation with tracing output, for example, the rcu:rcu_callback trace event. Reported-by: Vegard Nossum <vegard.nossum@oracle.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Eliminate the unused __rcu_is_watching() functionPaul E. McKenney2017-06-081-15/+4
| | | | | | | | | | The __rcu_is_watching() function is currently not used, aside from to implement the rcu_is_watching() function. This commit therefore eliminates __rcu_is_watching(), which has the beneficial side-effect of shrinking include/linux/rcupdate.h a bit. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Move docbook comments out of rcupdate.hPaul E. McKenney2017-06-081-4/+38
| | | | | | | | | | | | | | | The include/linux/rcupdate.h file is included by more than 200 files, so shrinking it should provide some build-time benefits. This commit therefore moves several docbook comments from rcupdate.h to kernel/rcu/update.c, kernel/rcu/tree.c, and kernel/rcu/tree_plugin.h, thus reducing the number of times that the compiler has to scan these comments. This likely provides only a small benefit, but every little bit helps. This commit also fixes a malformed bulleted list noted by the 0day Test Robot. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add lockdep_assert_held() teeth to tree.cPaul E. McKenney2017-06-081-0/+25
| | | | | | | | | Comments can be helpful, but assertions carry more force. This commit therefore adds lockdep_assert_held() and RCU_LOCKDEP_WARN() calls to enforce lock-held and interrupt-disabled preconditions. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Update rcu_bootup_announce_oddness()Paul E. McKenney2017-06-081-3/+6
| | | | | | | This commit updates rcu_bootup_announce_oddness() to check additional Kconfig options and module/boot parameters. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add preemptibility checks in rcu_sched_qs() and rcu_bh_qs()Paul E. McKenney2017-06-081-0/+2
| | | | | | | | | This commit adds WARN_ON_ONCE() calls that trigger if either rcu_sched_qs() or rcu_bh_qs() are invoked with preemption enabled. In the immortal words of Peter Zijlstra: "these are much harder to ignore than comments". Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove obsolete reference to synchronize_kernel()Paul E. McKenney2017-06-081-6/+0
| | | | | | | | | | | | | The synchronize_kernel() primitive was removed in favor of synchronize_sched() more than a decade ago, and it seems likely that rather few kernel hackers are familiar with it. Its continued presence is therefore providing more confusion than enlightenment. This commit therefore removes the reference from the synchronize_sched() header comment, and adds the corresponding information to the synchronize_rcu(0 header comment. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Complain if blocking in preemptible RCU read-side critical sectionPaul E. McKenney2017-06-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | Although preemptible RCU allows its read-side critical sections to be preempted, general blocking is forbidden. The reason for this is that excessive preemption times can be handled by CONFIG_RCU_BOOST=y, but a voluntarily blocked task doesn't care how high you boost its priority. Because preemptible RCU is a global mechanism, one ill-behaved reader hurts everyone. Hence the prohibition against general blocking in RCU-preempt read-side critical sections. Preemption yes, blocking no. This commit enforces this prohibition. There is a special exception for the -rt patchset (which they kindly volunteered to implement): It is OK to block (as opposed to merely being preempted) within an RCU-preempt read-side critical section, but only if the blocking is subject to priority inheritance. This exception permits CONFIG_RCU_BOOST=y to get -rt RCU readers out of trouble. Why doesn't this exception also apply to mainline's rt_mutex? Because of the possibility that someone does general blocking while holding an rt_mutex. Yes, the priority boosting will affect the rt_mutex, but it won't help with the task doing general blocking while holding that rt_mutex. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Prevent rcu_barrier() from starting needless grace periodsPaul E. McKenney2017-06-081-2/+8
| | | | | | | | | | | | | | | Currently rcu_barrier() uses call_rcu() to enqueue new callbacks on each CPU with a non-empty callback list. This works, but means that rcu_barrier() forces grace periods that are not otherwise needed. The key point is that rcu_barrier() never needs to wait for a grace period, but instead only for all pre-existing callbacks to be invoked. This means that rcu_barrier()'s new callbacks should be placed in the callback-list segment containing the last pre-existing callback. This commit makes this change using the new rcu_segcblist_entrain() function. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* Merge branch 'core-rcu-for-linus' of ↵Linus Torvalds2017-05-101-417/+293
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU updates from Ingo Molnar: "The main changes are: - Debloat RCU headers - Parallelize SRCU callback handling (plus overlapping patches) - Improve the performance of Tree SRCU on a CPU-hotplug stress test - Documentation updates - Miscellaneous fixes" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (74 commits) rcu: Open-code the rcu_cblist_n_lazy_cbs() function rcu: Open-code the rcu_cblist_n_cbs() function rcu: Open-code the rcu_cblist_empty() function rcu: Separately compile large rcu_segcblist functions srcu: Debloat the <linux/rcu_segcblist.h> header srcu: Adjust default auto-expediting holdoff srcu: Specify auto-expedite holdoff time srcu: Expedite first synchronize_srcu() when idle srcu: Expedited grace periods with reduced memory contention srcu: Make rcutorture writer stalls print SRCU GP state srcu: Exact tracking of srcu_data structures containing callbacks srcu: Make SRCU be built by default srcu: Fix Kconfig botch when SRCU not selected rcu: Make non-preemptive schedule be Tasks RCU quiescent state srcu: Expedite srcu_schedule_cbs_snp() callback invocation srcu: Parallelize callback handling kvm: Move srcu_struct fields to end of struct kvm rcu: Fix typo in PER_RCU_NODE_PERIOD header comment rcu: Use true/false in assignment to bool rcu: Use bool value directly ...
| * rcu: Open-code the rcu_cblist_n_lazy_cbs() functionPaul E. McKenney2017-05-021-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | Because the rcu_cblist_n_lazy_cbs() just samples the ->len_lazy counter, and because the rcu_cblist structure is quite straightforward, it makes sense to open-code rcu_cblist_n_lazy_cbs(p) as p->len_lazy, cutting out a level of indirection. This commit makes this change. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org>
| * rcu: Open-code the rcu_cblist_n_cbs() functionPaul E. McKenney2017-05-021-5/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | Because the rcu_cblist_n_cbs() just samples the ->len counter, and because the rcu_cblist structure is quite straightforward, it makes sense to open-code rcu_cblist_n_cbs(p) as p->len, cutting out a level of indirection. This commit makes this change. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org>
| * rcu: Open-code the rcu_cblist_empty() functionPaul E. McKenney2017-05-021-5/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | Because the rcu_cblist_empty() just samples the ->head pointer, and because the rcu_cblist structure is quite straightforward, it makes sense to open-code rcu_cblist_empty(p) as !p->head, cutting out a level of indirection. This commit makes this change. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org>
| * srcu: Make rcutorture writer stalls print SRCU GP statePaul E. McKenney2017-04-261-8/+4
| | | | | | | | | | | | | | | | | | | | | | In the past, SRCU was simple enough that there was little point in making the rcutorture writer stall messages print the SRCU grace-period number state. With the advent of Tree SRCU, this has changed. This commit therefore makes Classic, Tiny, and Tree SRCU report this state to rcutorture as needed. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Mike Galbraith <efault@gmx.de>
| *-. Merge branches 'doc.2017.04.12a', 'fixes.2017.04.19a' and 'srcu.2017.04.21a' ↵Paul E. McKenney2017-04-211-407/+289
| |\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | into HEAD doc.2017.04.12a: Documentation updates fixes.2017.04.19a: Miscellaneous fixes srcu.2017.04.21a: Parallelize SRCU callback handling
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