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* doc: Fix "struction" typo in RCU memory-ordering documentationJoel Fernandes (Google)2018-11-121-1/+1
| | | | | | | This commit replaces "struction" with the correct "structure". Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: RCU scheduler spinlock rcu_read_unlock() restriction remainsPaul E. McKenney2018-11-121-15/+29
| | | | | | | | | | | | | | | | Given RCU flavor consolidation, when rcu_read_unlock() is invoked with interrupts disabled, the reporting of the corresponding quiescent state is deferred until interrupts are re-enabled. There was therefore some hope that this would allow dropping the restriction against holding scheduler spinlocks across an rcu_read_unlock() without disabling interrupts across the entire corresponding RCU read-side critical section. Unfortunately, the need to quickly provide a quiescent state to expedited grace periods sometimes requires a call to raise_softirq() during rcu_read_unlock() execution. Because raise_softirq() can sometimes acquire the scheduler spinlocks, the restriction must remain in effect. This commit therefore updates the RCU requirements documentation accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Make listing in RCU perf/scale requirements use rcu_assign_pointer()Joel Fernandes (Google)2018-11-121-1/+1
| | | | | | | | | | The code listing under this section has a quick quiz that says line 19 uses rcu_access_pointer, but the code listing itself instead uses rcu_dereference(). This commit therefore makes the code listing match the quick quiz. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Remove obsolete (non-)requirement about disabling preemptionJoel Fernandes (Google)2018-11-121-50/+0
| | | | | | | | | | The Requirements.html document says "Disabling Preemption Does Not Block Grace Periods". However this is no longer true with the RCU consolidation. This commit therefore removes the obsolete (non-)requirement entirely. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: rcu: Update description of gp_seq fields in rcu_dataJoel Fernandes (Google)2018-11-121-3/+4
| | | | | | | | | The rcu_state structure doesn't have a gp_seq_needed field. Update the description under rcu_data accordingly, to reflect this. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: rcu: Better clarify the rcu_segcblist ->len fieldJoel Fernandes (Google)2018-11-121-8/+15
| | | | | | | | | | | An important note under the rcu_segcblist description could use a more detailed description. Especially explanation of the scenario where the ->head field may be temporarily NULL making it not wise to rely on it to determine if callbacks are associated with the rcu_segcblist. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: rcu: Update Data-Structures for RCU flavor consolidationJoel Fernandes (Google)2018-11-125-2240/+559
| | | | | | | | | | This patch updates all Data-Structures document figures and text and removes some unwanted figures, to reflect the recent work Paul has been doing with consolidating all flavors of RCU. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Remove rcu_dynticks from Data-StructuresJoel Fernandes (Google)2018-11-122-760/+25
| | | | | | | | | rcu_dynticks was folded into rcu_data structure. Update the data structures RCU document accordingly. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Update information about resched_cpuJoel Fernandes (Google)2018-11-121-3/+3
| | | | | | | | | | Since commit fced9c8cfe6b ("rcu: Avoid resched_cpu() when rescheduling the current CPU"), resched_cpu is not directly called from sync_sched_exp_handler. Update the documentation about the same. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Clarify RCU data-structure comment about rcu_tree fanoutJoel Fernandes (Google)2018-11-081-3/+5
| | | | | | | | | | | | RCU Data-Structures document describes a trick to test RCU with small number of CPUs but with a taller tree. It wasn't immediately clear how the document arrived at 16 CPUs which also requires setting the FANOUT_LEAF to 2 instead of the default of 16. This commit therefore provides the needed clarification. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <kernel-team@android.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
* doc: Set down forward-progress requirementsPaul E. McKenney2018-11-081-2/+108
| | | | | | | This commit adds a section to the requirements documentation setting down requirements for grace-period and callback-invocation forward progress. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*-. Merge branches 'doc.2018.08.30a', 'dynticks.2018.08.30b', 'srcu.2018.08.30b' ↵Paul E. McKenney2018-08-301-26/+24
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | and 'torture.2018.08.29a' into HEAD doc.2018.08.30a: Documentation updates dynticks.2018.08.30b: RCU flavor consolidation updates and cleanups srcu.2018.08.30b: SRCU updates torture.2018.08.29a: Torture-test updates
| * | rcu: Defer reporting RCU-preempt quiescent states when disabledPaul E. McKenney2018-08-301-26/+24
| |/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit defers reporting of RCU-preempt quiescent states at rcu_read_unlock_special() time when any of interrupts, softirq, or preemption are disabled. These deferred quiescent states are reported at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug offline operation. Of course, if another RCU read-side critical section has started in the meantime, the reporting of the quiescent state will be further deferred. This also means that disabling preemption, interrupts, and/or softirqs will act as an RCU-preempt read-side critical section. This is enforced by checking preempt_count() as needed. Some special cases must be handled on an ad-hoc basis, for example, context switch is a quiescent state even though both the scheduler and do_exit() disable preemption. In these cases, additional calls to rcu_preempt_deferred_qs() override the preemption disabling. Similar logic overrides disabled interrupts in rcu_preempt_check_callbacks() because in this case the quiescent state happened just before the corresponding scheduling-clock interrupt. In theory, this change lifts a long-standing restriction that required that if interrupts were disabled across a call to rcu_read_unlock() that the matching rcu_read_lock() also be contained within that interrupts-disabled region of code. Because the reporting of the corresponding RCU-preempt quiescent state is now deferred until after interrupts have been enabled, it is no longer possible for this situation to result in deadlocks involving the scheduler's runqueue and priority-inheritance locks. This may allow some code simplification that might reduce interrupt latency a bit. Unfortunately, in practice this would also defer deboosting a low-priority task that had been subjected to RCU priority boosting, so real-time-response considerations might well force this restriction to remain in place. Because RCU-preempt grace periods are now blocked not only by RCU read-side critical sections, but also by disabling of interrupts, preemption, and softirqs, it will be possible to eliminate RCU-bh and RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels. This may require some additional plumbing to provide the network denial-of-service guarantees that have been traditionally provided by RCU-bh. Once these are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh into RCU-sched. This would mean that all kernels would have but one flavor of RCU, which would open the door to significant code cleanup. Moving to a single flavor of RCU would also have the beneficial effect of reducing the NOCB kthreads by at least a factor of two. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback from Joel Fernandes. ] [ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in response to bug reports from kbuild test robot. ] [ paulmck: Fix bug located by kbuild test robot involving recursion via rcu_preempt_deferred_qs(). ]
* | doc: Fix broken HTML directivePaul E. McKenney2018-08-301-1/+1
| | | | | | | | | | | | This commit adds the needed "<". Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Update removal of RCU-bh/sched update machineryPaul E. McKenney2018-08-303-134/+45
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The RCU-bh update API is now defined in terms of that of RCU-bh and RCU-sched, so this commit updates the documentation accordingly. In addition, although RCU-sched persists in !PREEMPT kernels, in the PREEMPT case its update API is now defined in terms of that of RCU-preempt, so this commit also updates the documentation accordingly. While in the area, this commit removes the documentation for the now-obsolete synchronize_rcu_mult() and clarifies the Tasks RCU documentation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Improve rcu_dynticks::dynticks documentationJoel Fernandes (Google)2018-08-291-3/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The very useful RCU Data-Structures describes that the dynticks counter of the rcu_dynticks data structure is incremented when we transitions to or from dynticks-idle mode. However it doesn't mention that it is also incremented due to transitions to and from user mode which for dynticks purposes is an extended quiescent state. I found this with tracing calls to rcu_dynticks_eqs_enter which can also happen from rcu_user_enter. Lets add this information to the Data-Structures document. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Fix broken RCU-requirements link to LKML archiveJoel Fernandes (Google)2018-08-291-2/+2
| | | | | | | | | | | | | | | | Two of the Requirements.html LKML links are broken. This patch changes them to use the archive from lore.kernel.org, which works fine. Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Add design documentation on interruption of NMI handlersPaul E. McKenney2018-08-291-0/+11
|/ | | | | | | Make Requirements.html talk about how NMI handlers can take what appear to RCU to be normal interrupts. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Update memory-ordering documentation for ->gp-seqPaul E. McKenney2018-07-126-223/+243
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Update data-structure documentation for ->gp_seqPaul E. McKenney2018-07-121-55/+63
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*---. Merge branches 'cond_resched.2017.12.04a', 'dyntick.2017.11.28a', ↵Paul E. McKenney2017-12-112-15/+34
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'fixes.2017.12.11a', 'srbd.2017.12.05a' and 'torture.2017.12.11a' into HEAD cond_resched.2017.12.04a: Convert cond_resched_rcu_qs() to cond_resched() dyntick.2017.11.28a: Make RCU dynticks handle interrupts from NMI fixes.2017.12.11a: Miscellaneous fixes srbd.2017.12.05a: Remove now-redundant smp_read_barrier_depends() torture.2017.12.11a: Torture-testing update
| | | * doc: De-emphasize smp_read_barrier_dependsPaul E. McKenney2017-12-051-1/+2
| | |/ | | | | | | | | | | | | | | | | | | | | | This commit keeps only the historical and low-level discussion of smp_read_barrier_depends(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
| * / doc: Update dyntick-idle design documentation for NMI/irq consolidationPaul E. McKenney2017-11-281-14/+32
| |/ | | | | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* / doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()Paul E. McKenney2017-12-042-3/+4
|/ | | | | | | | Now that cond_resched() also provides RCU quiescent states when needed, it can be used in place of cond_resched_rcu_qs(). This commit therefore documents this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* Merge branch 'core-rcu-for-linus' of ↵Linus Torvalds2017-11-1314-0/+14170
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU updates from Ingo Molnar: "The main changes in this cycle are: - Documentation updates - RCU CPU stall-warning updates - Torture-test updates - Miscellaneous fixes Size wise the biggest updates are to documentation. Excluding documentation most of the code increase comes from a single commit which expands debugging" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) srcu: Add parameters to SRCU docbook comments doc: Rewrite confusing statement about memory barriers memory-barriers.txt: Fix typo in pairing example rcu/segcblist: Include rcupdate.h rcu: Add extended-quiescent-state testing advice rcu: Suppress lockdep false-positive ->boost_mtx complaints rcu: Do not include rtmutex_common.h unconditionally torture: Provide TMPDIR environment variable to specify tmpdir rcutorture: Dump writer stack if stalled rcutorture: Add interrupt-disable capability to stall-warning tests rcu: Suppress RCU CPU stall warnings while dumping trace rcu: Turn off tracing before dumping trace rcu: Make RCU CPU stall warnings check for irq-disabled CPUs sched,rcu: Make cond_resched() provide RCU quiescent state sched: Make resched_cpu() unconditional irq_work: Map irq_work_on_queue() to irq_work_on() in !SMP rcu: Create call_rcu_tasks() kthread at boot time rcu: Fix up pending cbs check in rcu_prepare_for_idle memory-barriers: Rework multicopy-atomicity section memory-barriers: Replace uses of "transitive" ...
| * documentation: RCU grace-period memory ordering guaranteesPaul E. McKenney2017-10-0914-0/+14170
| | | | | | | | | | | | | | | | | | This commit provides text and diagrams showing how Tree RCU implements its grace-period memory ordering guarantees. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Linus Torvalds <torvalds@linux-foundation.org>
* | Documentation: fix ref to workqueue contentTom Saeger2017-10-191-1/+1
|/ | | | | Signed-off-by: Tom Saeger <tom.saeger@oracle.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
* doc: Set down RCU's scheduling-clock-interrupt needsPaul E. McKenney2017-08-171-0/+130
| | | | | | | | This commit documents the situations in which RCU needs the scheduling-clock interrupt to be enabled, along with the consequences of failing to meet RCU's needs in this area. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove debugfs tracingPaul E. McKenney2017-06-081-1/+1
| | | | | | | | | RCU's debugfs tracing used to be the only reasonable low-level debug information available, but ftrace and event tracing has since surpassed the RCU debugfs level of usefulness. This commit therefore removes RCU's debugfs tracing. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Remove SPARSE_RCU_POINTER Kconfig optionPaul E. McKenney2017-06-081-6/+3
| | | | | | | | | | | The sparse-based checking for non-RCU accesses to RCU-protected pointers has been around for a very long time, and it is now the only type of sparse-based checking that is optional. This commit therefore makes it unconditional. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
* rcu: Remove nohz_full full-system-idle state machinePaul E. McKenney2017-06-081-5/+1
| | | | | | | | | | | | | | 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>
* doc: Take tail recursion into account in RCU requirementsPaul E. McKenney2017-06-081-1/+2
| | | | | | | This commit classifies tail recursion as an alternative way to write a loop, with similar limitations. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* srcu: Document auto-expediting requirementPaul E. McKenney2017-06-081-0/+14
| | | | | | | | This commit documents the auto-expediting requirement satisfied by commits 2da4b2a7fd8d ("srcu: Expedite first synchronize_srcu() when idle") and 22607d66bbc3 ("srcu: Specify auto-expedite holdoff time"). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*-. Merge branches 'doc.2017.04.12a', 'fixes.2017.04.19a' and 'srcu.2017.04.21a' ↵Paul E. McKenney2017-04-211-1/+25
|\ \ | | | | | | | | | | | | | | | | | | | | | into HEAD doc.2017.04.12a: Documentation updates fixes.2017.04.19a: Miscellaneous fixes srcu.2017.04.21a: Parallelize SRCU callback handling
| | * rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actionsPaul E. McKenney2017-04-181-1/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_all_qs() and rcu_note_context_switch() do a series of checks, taking various actions to supply RCU with quiescent states, depending on the outcomes of the various checks. This is a bit much for scheduling fastpaths, so this commit creates a separate ->rcu_urgent_qs field in the rcu_dynticks structure that acts as a global guard for these checks. Thus, in the common case, rcu_all_qs() and rcu_note_context_switch() check the ->rcu_urgent_qs field, find it false, and simply return. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org>
| | * rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()Paul E. McKenney2017-04-181-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking that one of them still needs a quiescent state before doing an expensive atomic operation on the ->dynticks counter. However, this check reduces overhead only after a rare race condition, and increases complexity. This commit therefore removes the scan and the mechanism enabling the scan. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Pull rcu_qs_ctr into rcu_dynticks structurePaul E. McKenney2017-04-181-2/+10
| | | | | | | | | | | | | | | | | | | | | | | | The rcu_qs_ctr variable is yet another isolated per-CPU variable, so this commit pulls it into the pre-existing rcu_dynticks per-CPU structure. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Pull rcu_sched_qs_mask into rcu_dynticks structurePaul E. McKenney2017-04-181-1/+8
| |/ | | | | | | | | | | | | | | The rcu_sched_qs_mask variable is yet another isolated per-CPU variable, so this commit pulls it into the pre-existing rcu_dynticks per-CPU structure. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Update requirements based on recent changesPaul E. McKenney2017-04-121-26/+94
| | | | | | | | | | | | | | | | | | | | | | These changes include lighter-weight expedited grace periods, the fact that expedited grace periods and rcu_barrier() no longer block CPU hotplug, some HTML font fixups, noting that rcu_barrier() need not wait for a grace period (even if callbacks are posted), the fact that SRCU read-side critical sections can be used from offline CPUs, and the fact that SRCU now maintains per-CPU callback lists. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Update RCU data-structure documentation for rcu_segcblistPaul E. McKenney2017-04-122-85/+156
| | | | | | | | | | | | | | | | The rcu_segcblist data structure, which contains segmented lists of RCU callbacks, was recently added. This commit updates the documentation accordingly. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Add mid-boot operation to expedited grace periodsPaul E. McKenney2017-04-121-3/+44
| | | | | | | | | | | | | | | | | | | | | | | | | | This commit adds a description of how expedited grace periods operate during the mid-boot "dead zone", which starts when the scheduler spawns the first kthread and ends when all of RCU's kthreads have been spawned. In short, before mid-boot, synchronous grace periods can be a no-op. After the end of mid-boot, workqueues may be used. During mid-boot, the requesting task drivees the expedited grace period. For more detail, see https://lwn.net/Articles/716148/. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | doc: Synchronous RCU grace periods are now legal throughout bootPaul E. McKenney2017-04-121-34/+47
|/ | | | | | | | This commit updates the "Early Boot" section of the RCU requirements to describe how synchronous RCU grace periods are now legal throughout the boot process. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* doc: Quick-Quiz answers are now inlinePaul E. McKenney2017-01-141-4/+1
| | | | | | | | | Now that quick-quiz answers are inline, there is no separate section containing those answers. This commit therefore removes the dangling reference from the RCU data-structures design documentation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* doc: Fix RCU requirements typosTetsuo Handa2017-01-141-6/+6
| | | | | | Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Design documentation for expedited grace periodsPaul E. McKenney2017-01-1412-0/+5093
| | | | | | | | | | | | | | This commit adds design documentation for expedited grace periods. This documentation is in HTML rather than the new documentation format because (1) I have prototype documentation already in HTML, and (2) Attempting to learn the new documentation format while creating the design documentation seems likely to result in neither happening in a timely fashion. Once the design documentation is complete, we can start a conversion effort. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* documentation: Present updated RCU guaranteePaul E. McKenney2016-11-141-1/+24
| | | | | | | | | Recent memory-model work deduces the relationships of RCU read-side critical sections and grace periods based on the relationships of accesses within a critical section and accesses preceding and following the grace period. This commit therefore adds this viewpoint. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Record reason for rcu_head two-byte alignmentPaul E. McKenney2016-08-221-0/+22
| | | | | | | | | | | | There is an assertion in __call_rcu() that checks only the bottom bit of the rcu_head pointer, rather than the bottom two (as might be expected for 32-bit systems) or the bottom three (as might be expected for 64-bit systems). This choice might be a bit surprising in these days of ubiquitous 32-bit and 64-bit systems. This commit therefore records the reason for this odd alignment check, namely that m68k guarantees only two-byte alignment despite being a 32-bit architectures. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Add RCU_NONIDLE() restrictions to requirementsPaul E. McKenney2016-06-141-0/+35
| | | | Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Add documentation for RCU's major data structuresPaul E. McKenney2016-04-1912-0/+8291
| | | | | | | This commit adds documentation for RCU's major data structures, including rcu_state, rcu_node, rcu_data, rcu_dynticks, and rcu_head. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* documentation: Emphasize the call_rcu() is illegal from idlePaul E. McKenney2016-03-311-1/+1
| | | | | | | | | Although call_rcu()'s fastpath works just fine on an idle CPU, some branches of the slowpath invoke the scheduler, which uses RCU. Therefore, this commit emphasizes the fact that call_rcu() must not be invoked from an idle CPU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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