- Mar 26, 2019
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Paul E. McKenney authored
This commit fixes some issues with Documentation/RCU/checklist.txt. Signed-off-by:Paul E. McKenney <paulmck@linux.ibm.com>
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Paul E. McKenney authored
Reported-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
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Tycho Andersen authored
A diagram in whatisRCU.txt has space character before tabs. This commit therefore makes this diagram consistent with elsewhere in the document: Use one leading tab, followed by spaces for any additional whitespace required. Signed-off-by:
Tycho Andersen <tycho@tycho.ws> Signed-off-by:
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Paul E. McKenney authored
Now that synchronize_rcu_bh, synchronize_rcu_bh_expedited, call_rcu_bh, rcu_barrier_bh, synchronize_sched, synchronize_sched_expedited, call_rcu_sched, rcu_barrier_sched, get_state_synchronize_sched, and cond_synchronize_sched are obsolete, let's remove them from the documentation aside from a small historical section. Signed-off-by:
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- Mar 04, 2019
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Geert Uytterhoeven authored
Since the removal of FS_RECLAIM annotations, lockdep states contain four characters, not six. Fixes: e5684bbf ("Documentation/locking/lockdep: Update info about states") Fixes: d92a8cfc ("locking/lockdep: Rework FS_RECLAIM annotation") Signed-off-by:
Geert Uytterhoeven <geert+renesas@glider.be> Acked-by:
Will Deacon <will.deacon@arm.com> Signed-off-by:
Jonathan Corbet <corbet@lwn.net>
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Geert Uytterhoeven authored
Suspicious RCU usage messages are reported as warnings. Fixes: a5dd63ef ("lockdep: Use "WARNING" tag on lockdep splats") Signed-off-by:
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- Jan 25, 2019
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Junchang Wang authored
The supported module parameters are detailed in both RCU/torture.txt and admin-guide/kernel-parameters.txt, and the latter is actively maintained. So this patch removes section MODULE PARAMETERS in torture.txt and adds a reference to the information in kernel-parameters.txt. Signed-off-by:
Junchang Wang <junchangwang@gmail.com> Signed-off-by:
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Paul E. McKenney authored
Although the name rcu_process_callbacks() still makes sense for Tiny RCU, where most of what it does is invoke callbacks, it no longer makes much sense for Tree RCU, especially given that the actually callback invocation is relegated to rcu_do_batch(), or, for no-CBs CPUs, to the rcuo kthreads. Especially in the latter case, rcu_process_callbacks() has very little to do with actual callbacks. A better description of this function is that it performs RCU's core processing. This commit therefore changes the name of Tree RCU's rcu_process_callbacks() function to rcu_core(), which also has the virtue of being consistent with the existing invoke_rcu_core() function. While in the area, the header comment is reworked. Signed-off-by: -
Paul E. McKenney authored
The name rcu_check_callbacks() arguably made sense back in the early 2000s when RCU was quite a bit simpler than it is today, but it has become quite misleading, especially with the advent of dyntick-idle and NO_HZ_FULL. The rcu_check_callbacks() function is RCU's hook into the scheduling-clock interrupt, and is now but one of many ways that callbacks get promoted to invocable state. This commit therefore changes the name to rcu_sched_clock_irq(), which is the same number of characters and clearly indicates this function's relation to the rest of the Linux kernel. In addition, for the sake of consistency, rcu_flavor_check_callbacks() is also renamed to rcu_flavor_sched_clock_irq(). While in the area, the header comments for both functions are reworked. Signed-off-by: -
Junchang Wang authored
Fix outdated links in whatisRCU.txt. Signed-off-by:
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Paul E. McKenney authored
SRCU's synchronize_srcu() may not be invoked from CPU-hotplug notifiers, due to the fact that SRCU grace periods make use of timers and the possibility of timers being temporarily stranded on the outgoing CPU. This stranding of timers means that timers posted to the outgoing CPU will not fire until late in the CPU-hotplug process. The problem is that if a notifier is waiting on an SRCU grace period, that grace period is waiting on a timer, and that timer is stranded on the outgoing CPU, then the notifier will never be awakened, in other words, deadlock has occurred. This same situation of course also prohibits srcu_barrier() from being invoked from CPU-hotplug notifiers. This commit therefore updates the requirements to include this restriction. Signed-off-by: -
Paul E. McKenney authored
Back when there were multiple flavors of RCU, it was necessary to separately count lazy and non-lazy callbacks for each CPU. These counts were used in CONFIG_RCU_FAST_NO_HZ kernels to determine how long a newly idle CPU should be allowed to sleep before handling its RCU callbacks. But now that there is only one flavor, the callback counts for a given CPU's sole rcu_data structure are the counts for that CPU. This commit therefore removes the rcu_data structure's ->nonlazy_posted and ->nonlazy_posted_snap fields, the rcu_idle_count_callbacks_posted() and rcu_cpu_has_callbacks() functions, repurposes the rcu_data structure's ->all_lazy field to record the laziness state at the beginning of the latest idle sojourn, and modifies CONFIG_RCU_FAST_NO_HZ RCU CPU stall warnings accordingly. Signed-off-by: -
Paul E. McKenney authored
Back when there could be multiple RCU flavors running in the same kernel at the same time, it was necessary to specify the expedited grace-period IPI handler at runtime. Now that there is only one RCU flavor, the IPI handler can be determined at build time. There is therefore no longer any reason for the RCU-preempt and RCU-sched IPI handlers to have different names, nor is there any reason to pass these handlers in function arguments and in the data structures enclosing workqueues. This commit therefore makes all these changes, pushing the specification of the expedited grace-period IPI handler down to the point of use. Signed-off-by:
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- Nov 12, 2018
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Joel Fernandes (Google) authored
This commit replaces "struction" with the correct "structure". Signed-off-by:
Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:
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Joel Fernandes (Google) authored
The stallwarn document incorrectly mentions 'fps=' instead of 'fqs='. This commit orrects that. Signed-off-by:
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Paul E. McKenney authored
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: -
Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
The whatisRCU.txt document says rcu_dereference() cannot be used outside of rcu_read_lock() protected sections. The commit adds a mention of rcu_dereference_protected(), so that the new reader knows that this API can be used to avoid update-side use of rcu_read_lock() and rcu_read_unlock(). Cc: tytso@mit.edu Suggested-by:
<tytso@mit.edu> Signed-off-by:
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Joel Fernandes (Google) authored
The checklist suggests rcu_barrier_bh() for RCU-bh and similarly for sched, however these APIs are now implemented as rcu_barrier() itself due to the RCU consolidation. This commit therefore corrects checklist.txt to encourage use of the underlying rcu_barrier() API. Signed-off-by:
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Joel Fernandes (Google) authored
Since the RCU mechanisms have been consolidated, the checklist item warning that synchronize_rcu() waits only for RCU readers is obsolete. This commit therefore removes this checklist item. Signed-off-by:
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Joel Fernandes (Google) authored
call_rcu_bh is now implemented in terms of call_rcu, so the suggestion to use a different API for speed benefits is not accurate anymore. This commit updates the document accordingly. Signed-off-by:
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Joel Fernandes (Google) authored
This commit explains why rcu_read_lock_sched is better than using preempt_disable. Signed-off-by:
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Joel Fernandes (Google) authored
RCU consolidation effort causes the update side of the RCU API to be consistent across all the 3 RCU flavors (normal, sched, bh). This commit therefore updates the full API in the whatisRCU document, thus encouraging people to use the consolidated RCU update API instead of the old RCU-bh and RCU-sched update APIs. Also rcu_dereference is documented to be the same for all 3 mechanisms (even before the consolidation), however its actually different - as using the right rcu_dereference primitive (such as rcu_dereference_bh for bh) is needed to make lock debugging work correctly. This update also corrects that. Also, add local_bh_disable() and local_bh_enable() as softirq protection primitives and correct a grammar error in a quiz answer. Signed-off-by:
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Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
rcu_dynticks was folded into rcu_data structure. Update the data structures RCU document accordingly. Signed-off-by:
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Joel Fernandes (Google) authored
Since commit fced9c8c ("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:
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- Nov 09, 2018
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Joel Fernandes (Google) authored
Consolidation of RCU-bh, RCU-preempt, and RCU-sched into one RCU flavor to rule them all resulted in the removal of rcu_preempt_state. However, stallwarn.txt still mentions rcu_preempt_state. This commit therefore Updates stallwarn documentation accordingly. Signed-off-by:
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Joel Fernandes (Google) authored
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:
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Paul E. McKenney authored
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>
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- Sep 09, 2018
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Henrik Austad authored
This is a respin with a wider audience (all that get_maintainer returned) and I know this spams a *lot* of people. Not sure what would be the correct way, so my apologies for ruining your inbox. The 00-INDEX files are supposed to give a summary of all files present in a directory, but these files are horribly out of date and their usefulness is brought into question. Often a simple "ls" would reveal the same information as the filenames are generally quite descriptive as a short introduction to what the file covers (it should not surprise anyone what Documentation/sched/sched-design-CFS.txt covers) A few years back it was mentioned that these files were no longer really needed, and they have since then grown further out of date, so perhaps it is time to just throw them out. A short status yields the following _outdated_ 00-INDEX files, first counter is files listed in 00-INDEX but missing in the directory, last is files present but not listed in 00-INDEX. List of outdated 00-INDEX: Documentation: (4/10) Documentation/sysctl: (0/1) Documentation/timers: (1/0) Documentation/blockdev: (3/1) Documentation/w1/slaves: (0/1) Documentation/locking: (0/1) Documentation/devicetree: (0/5) Documentation/power: (1/1) Documentation/powerpc: (0/5) Documentation/arm: (1/0) Documentation/x86: (0/9) Documentation/x86/x86_64: (1/1) Documentation/scsi: (4/4) Documentation/filesystems: (2/9) Documentation/filesystems/nfs: (0/2) Documentation/cgroup-v1: (0/2) Documentation/kbuild: (0/4) Documentation/spi: (1/0) Documentation/virtual/kvm: (1/0) Documentation/scheduler: (0/2) Documentation/fb: (0/1) Documentation/block: (0/1) Documentation/networking: (6/37) Documentation/vm: (1/3) Then there are 364 subdirectories in Documentation/ with several files that are missing 00-INDEX alltogether (and another 120 with a single file and no 00-INDEX). I don't really have an opinion to whether or not we /should/ have 00-INDEX, but the above 00-INDEX should either be removed or be kept up to date. If we should keep the files, I can try to keep them updated, but I rather not if we just want to delete them anyway. As a starting point, remove all index-files and references to 00-INDEX and see where the discussion is going. Signed-off-by:
Henrik Austad <henrik@austad.us> Acked-by:
Steven Rostedt <rostedt@goodmis.org> Reviewed-by:
Jens Axboe <axboe@kernel.dk> Acked-by:
Paul Moore <paul@paul-moore.com> Acked-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by:
Mark Brown <broonie@kernel.org> Acked-by:
Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: [Almost everybody else] Signed-off-by:
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- Aug 30, 2018
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Paul E. McKenney authored
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 authored
This commit adds the needed "<". Signed-off-by: -
Paul E. McKenney authored
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:
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- Aug 29, 2018
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Joel Fernandes (Google) authored
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:
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Joel Fernandes (Google) authored
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:
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Paul E. McKenney authored
Make Requirements.html talk about how NMI handlers can take what appear to RCU to be normal interrupts. Signed-off-by:
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- Jul 12, 2018
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NeilBrown authored
Unfortunately the patch for adding list_for_each_entry_from_rcu() wasn't the final patch after all review. It is functionally correct but the documentation was incomplete. This patch adds this missing documentation which includes an update to the documentation for list_for_each_entry_continue_rcu() to match the documentation for the new list_for_each_entry_from_rcu(), and adds list_for_each_entry_from_rcu() and the already existing hlist_for_each_entry_from_rcu() to section 7 of whatisRCU.txt. Reviewed-by:
NeilBrown <neilb@suse.com> Signed-off-by:
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