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2016-03-31rcu: Remove expedited GP funnel-lock bypassPaul E. McKenney
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 <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Emphasize the call_rcu() is illegal from idlePaul E. McKenney
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>
2016-03-31documentation: Sharpen up the no-readers quick quizPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Get rid of duplicate .htmlx filePaul E. McKenney
This commit uses colors to obscure the quick-quiz answers, thus getting rid of the .htmlx file. Use your mouse to select the answer in order to see the text. Alternatively, use your favorite scripting language to remove all occurences of "<font color="ffffff">" from the file. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Remove unnecessary images from requirementsPaul E. McKenney
This commit removes a cutesy cartoon and also a diagram that can just as easily be represented by text. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Document illegality of call_rcu() from offline CPUsPaul E. McKenney
There is already a blanket statement about no member of RCU's API being legal from an offline CPU, but add an explicit note where it states that it is illegal to invoke call_rcu() from an NMI handler. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Explain why rcu_read_lock() needs no barrier()Paul E. McKenney
This commit adds a Quick Quiz whose answer explains why the compiler code reordering enabled by CONFIG_PREEMPT=n's empty rcu_read_lock() and rcu_read_unlock() functions does not hinder RCU's ability to figure out which RCU read-side critical sections have completed and not. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Add synchronize_rcu_mult() to the requirementsPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Add real-time requirements from CPU-bound workloadsPaul E. McKenney
This commit records RCU's responsibility to avoid degrading latencies of CPUs running tight loops within properly configured workloads, both in kernel and in userspace. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Make sample code and documentation consistentYao Dongdong
In the chapter 'analogy with reader-writer locking', the sample code uses spinlock_t in reader-writer case. Just correct it so that we can read the document easily. Signed-off-by: Yao Dongdong <yaodongdong@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Update RCU requirements based on expedited changesPaul E. McKenney
Because RCU-sched expedited grace periods now use IPIs and interact with rcu_read_unlock(), it is no longer sufficient to disable preemption across RCU read-side critical sections that acquire and hold scheduler locks. It is now necessary to instead disable interrupts. This commit documents this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Clarify RCU memory barriers and requirementsPaul E. McKenney
The RCU requirements do not make it absolutely clear that the memory-barrier requirements are not intended to replace the fundamental requirement that all pre-existing RCU readers complete before a grace period completes. This commit therefore pulls the memory-barrier requirements into a separate section and explicitly calls out the relationship between the memory-barrier requirements and the fundamental requirement. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Expand on scheduler/RCU deadlock requirementsPaul E. McKenney
This commit adds a second option for avoiding scheduler/RCU deadlocks, namely that preemption be disabled across the entire RCU read-side critical section in question. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Composability analogiesPaul E. McKenney
This commit expands on RCU's composability by comparing it to that of transactional memory and of locking. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Cover requirements controlling stall warningsPaul E. McKenney
This commit adds verbiage on boot and sysfs parameters that can be used to control RCU CPU stall warnings, both to change the timeout and to suppress these warnings entirely. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05Documentation: Record bottom-bit-zero guarantee for ->nextPaul E. McKenney
This commit records RCU's guarantee that the bottom bit of the rcu_head structure's ->next field will remain zero for callbacks posted via call_rcu(), but not necessarily for <tt>kfree_rcu()</tt> or some possible future call_rcu_lazy() variant that might one day be created for energy-efficiency purposese. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Updates URLs as suggested by Josh Triplett. ]
2015-12-05documentation: Record RCU requirementsPaul E. McKenney
This commit adds RCU requirements as published in a 2015 LWN series. Bringing these requirements in-tree allows them to be updated as changes are discovered. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Updates to charset and URLs as suggested by Josh Triplett. ]
2015-10-07Merge branches 'doc.2015.10.06a', 'percpu-rwsem.2015.10.06a' and ↵Paul E. McKenney
'torture.2015.10.06a' into HEAD doc.2015.10.06a: Documentation updates. percpu-rwsem.2015.10.06a: Optimization of per-CPU reader-writer semaphores. torture.2015.10.06a: Torture-test updates.
2015-10-06documentation: Catch up list of torture_type optionsPaul E. McKenney
This commit rids the documentation of long-obsolete torture_type options such as rcu_sync and adds new ones such as tasks. Also add verbiage noting the fact that rcutorture now concurrently tests the asynchrounous, synchronous, expedited synchronous, and polling grace-period primitives. Reported-by: David Miller <davem@davemloft.net> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David Miller <davem@davemloft.net> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06documentation: Correct doc to use rcu_dereference_protectedJason A. Donenfeld
As there is lots of misinformation and outdated information on the Internet about nearly all topics related to the kernel, I thought it would be best if I based my RCU code on the guidelines of the examples in the Documentation/ tree of the latest kernel. One thing that stuck out when reading the whatisRCU.txt document was, "interesting how we don't need any function to dereference rcu protected pointers when doing updates if a lock is held. I wonder how static analyzers will work with that." Then, a few weeks later, upon discovering sparse's __rcu support, I ran it over my code, and lo and behold, things weren't done right. Examining other RCU usages in the kernel reveal consistent usage of rcu_dereference_protected, passing in lockdep_is_held as the conditional. So, this patch adds that idiom to the documentation, so that others ahead of me won't endure the same exercise. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06documentation: Call out slow consoles as cause of stall warningsPaul E. McKenney
The Linux kernel outputs copious text during boot, and a slow serial console can result in stall warnings, particularly when messages are printed with interrupts disabled. This commit adds this to the list of causes of RCU CPU stall warning messages. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-09-20rcu: Invert passed_quiesce and rename to cpu_no_qsPaul E. McKenney
This commit inverts the sense of the rcu_data structure's ->passed_quiesce field and renames it to ->cpu_no_qs. This will allow a later commit to use an "aggregate OR" operation to test expedited as well as normal grace periods without added overhead. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-08-04Merge branches 'doc.2015.07.15a' and 'torture.2015.07.15a' into HEADPaul E. McKenney
doc.2015.07.15a: Documentation updates. torture.2015.07.15a: Torture-test updates.
2015-08-04Merge branches 'fixes.2015.07.22a' and 'initexp.2015.08.04a' into HEADPaul E. McKenney
fixes.2015.07.22a: Miscellaneous fixes. initexp.2015.08.04a: Initialization and expedited updates. (Single branch due to conflicts.)
2015-07-22rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()Paul E. McKenney
This commit renames rcu_lockdep_assert() to RCU_LOCKDEP_WARN() for consistency with the WARN() series of macros. This also requires inverting the sense of the conditional, which this commit also does. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Ingo Molnar <mingo@kernel.org>
2015-07-17rcu: Add fastpath bypassing funnel lockingPaul E. McKenney
In the common case, there will be only one expedited grace period in the system at a given time, in which case it is not helpful to use funnel locking. This commit therefore adds a fastpath that bypasses funnel locking when the root ->exp_funnel_mutex is not held. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-17documentation: Describe new expedited stall warningsPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-17rcu: Remove CONFIG_RCU_CPU_STALL_INFOPaul E. McKenney
The CONFIG_RCU_CPU_STALL_INFO has been default-y for a couple of releases with no complaints, so it is time to eliminate this Kconfig option entirely, so that the long-form RCU CPU stall warnings cannot be disabled. This commit does just that. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-15documentation: Fix spelling of "operators"Paul E. McKenney
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-06-24Merge tag 'docs-for-linus' of git://git.lwn.net/linux-2.6Linus Torvalds
Pull documentation updates from Jonathan Corbet: "The main thing here is Ingo's big subdirectory documenting feature support for each architecture. Beyond that, it's the usual pile of fixes, tweaks, and small additions" * tag 'docs-for-linus' of git://git.lwn.net/linux-2.6: (79 commits) doc:md: fix typo in md.txt. Documentation/mic/mpssd: don't build x86 userspace when cross compiling Documentation/prctl: don't build tsc tests when cross compiling Documentation/vDSO: don't build tests when cross compiling Doc:ABI/testing: Fix typo in sysfs-bus-fcoe Doc: Docbook: Change wikipedia's URL from http to https in scsi.tmpl Doc: Change wikipedia's URL from http to https Documentation/kernel-parameters: add missing pciserial to the earlyprintk Doc:pps: Fix typo in pps.txt kbuild : Fix documentation of INSTALL_HDR_PATH Documentation: filesystems: updated struct file_operations documentation in vfs.txt kbuild: edit explanation of clean-files variable Doc: ja_JP: Fix typo in HOWTO Move freefall program from Documentation/ to tools/ Documentation: ARM: EXYNOS: Describe boot loaders interface Doc:nfc: Fix typo in nfc-hci.txt vfs: Minor documentation fix Doc: networking: txtimestamp: fix printf format warning Documentation, intel_pstate: Improve legacy mode internal governors description Documentation: extend use case for EXPORT_SYMBOL_GPL() ...
2015-06-22Doc: Change wikipedia's URL from http to httpsMasanari Iida
Recently wikipedia announced to secure access to the servers. Now all http access re-route to https. Signed-off-by: Masanari Iida <standby24x7@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2015-05-27Merge branches 'array.2015.05.27a', 'doc.2015.05.27a', 'fixes.2015.05.27a', ↵Paul E. McKenney
'hotplug.2015.05.27a', 'init.2015.05.27a', 'tiny.2015.05.27a' and 'torture.2015.05.27a' into HEAD array.2015.05.27a: Remove all uses of RCU-protected array indexes. doc.2015.05.27a: Docuemntation updates. fixes.2015.05.27a: Miscellaneous fixes. hotplug.2015.05.27a: CPU-hotplug updates. init.2015.05.27a: Initialization/Kconfig updates. tiny.2015.05.27a: Updates to Tiny RCU. torture.2015.05.27a: Torture-testing updates.
2015-05-27documentation: State that rcu_dereference() reloads pointerMilos Vyletel
Make a note stating that repeated calls of rcu_dereference() may not return the same pointer if update happens while in critical section. Reported-by: Jeff Haran <jeff.haran@citrix.com> Signed-off-by: Milos Vyletel <milos@redhat.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-05-27documentation: Update rcu_dereference.txt based on WG21 discussionsPaul E. McKenney
This commit provides another caveat for the care and feeding of pointers returned by rcu_dereference() that was pointed out in discussions within the C++ standards committee. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2015-05-27documentation: RCU-protected array indexes no longer supportedPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-15Merge branches 'doc.2015.01.07a', 'fixes.2015.01.15a', ↵Paul E. McKenney
'preempt.2015.01.06a', 'srcu.2015.01.06a', 'stall.2015.01.16a' and 'torture.2015.01.11a' into HEAD doc.2015.01.07a: Documentation updates. fixes.2015.01.15a: Miscellaneous fixes. preempt.2015.01.06a: Changes to handling of lists of preempted tasks. srcu.2015.01.06a: SRCU updates. stall.2015.01.16a: RCU CPU stall-warning updates and fixes. torture.2015.01.11a: RCU torture-test updates and fixes.
2015-01-15rcu: Add GP-kthread-starvation checks to CPU stall warningsPaul E. McKenney
This commit adds a message that is printed if the relevant grace-period kthread has not been able to run for the two seconds preceding the stall warning. (The two seconds is double the maximum interval between successive bouts of quiescent-state forcing.) Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-15rcu: Make cond_resched_rcu_qs() apply to normal RCU flavorsPaul E. McKenney
Although cond_resched_rcu_qs() only applies to TASKS_RCU, it is used in places where it would be useful for it to apply to the normal RCU flavors, rcu_preempt, rcu_sched, and rcu_bh. This is especially the case for workloads that aggressively overload the system, particularly those that generate large numbers of RCU updates on systems running NO_HZ_FULL CPUs. This commit therefore communicates quiescent states from cond_resched_rcu_qs() to the normal RCU flavors. Note that it is unfortunately necessary to leave the old ->passed_quiesce mechanism in place to allow quiescent states that apply to only one flavor to be recorded. (Yes, we could decrement ->rcu_qs_ctr_snap in that case, but that is not so good for debugging of RCU internals.) In addition, if one of the RCU flavor's grace period has stalled, this will invoke rcu_momentary_dyntick_idle(), resulting in a heavy-weight quiescent state visible from other CPUs. Reported-by: Sasha Levin <sasha.levin@oracle.com> Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Merge commit from Sasha Levin fixing a bug where __this_cpu() was used in preemptible code. ]
2015-01-06rcu: Improve diagnostics for spurious RCU CPU stall warningsPaul E. McKenney
The current RCU CPU stall warning code will print "Stall ended before state dump start" any time that the stall-warning code is triggered on a CPU that has already reported a quiescent state for the current grace period and if all quiescent states have been reported for the current grace period. However, a true stall can result in these symptoms, for example, by preventing RCU's grace-period kthreads from ever running This commit therefore checks for this condition, reporting the end of the stall only if one of the grace-period counters has actually advanced. Otherwise, it reports the last time that the grace-period kthread made meaningful progress. (In normal situations, the grace-period kthread should make meaningful progress at least every jiffies_till_next_fqs jiffies.) Reported-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Miroslav Benes <mbenes@suse.cz>
2015-01-06documentation: Update sysfs path for rcu_cpu_stall_timeoutXie XiuQi
Commit 6bfc09e2327d ("rcu: Provide RCU CPU stall warnings for tiny RCU") moved the rcu_cpu_stall_timeout module parameter from rcutree.c to rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This commit therefore repairs this omission. commit 96224daa16d6 ("documentation: Update sysfs path for rcu_cpu_stall_suppress") updated the path for rcu_cpu_stall_suppress, but failed to update for rcu_cpu_stall_timeout. Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-11-13Merge branches 'torture.2014.11.03a', 'cpu.2014.11.03a', 'doc.2014.11.13a', ↵Paul E. McKenney
'fixes.2014.11.13a', 'signal.2014.10.29a' and 'rt.2014.10.29a' into HEAD cpu.2014.11.03a: Changes for per-CPU variables. doc.2014.11.13a: Documentation updates. fixes.2014.11.13a: Miscellaneous fixes. signal.2014.10.29a: Signal changes. rt.2014.10.29a: Real-time changes. torture.2014.11.03a: torture-test changes.
2014-10-29rcu: Remove redundant TREE_PREEMPT_RCU config optionPranith Kumar
PREEMPT_RCU and TREE_PREEMPT_RCU serve the same function after TINY_PREEMPT_RCU has been removed. This patch removes TREE_PREEMPT_RCU and uses PREEMPT_RCU config option in its place. Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-10-28rcu: Remove CONFIG_RCU_CPU_STALL_VERBOSEPaul E. McKenney
The CONFIG_RCU_CPU_STALL_VERBOSE Kconfig parameter causes preemptible RCU's CPU stall warnings to dump out any preempted tasks that are blocking the current RCU grace period. This information is useful, and the default has been CONFIG_RCU_CPU_STALL_VERBOSE=y for some years. It is therefore time for this commit to remove this Kconfig parameter, so that future kernel builds will always act as if CONFIG_RCU_CPU_STALL_VERBOSE=y. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-09-07documentation: Add verbiage on RCU-tasks stall warning messagesPaul E. McKenney
This commit documents RCU-tasks stall warning messages and also describes when to use the new cond_resched_rcu_qs() API. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2014-08-06list: fix order of arguments for hlist_add_after(_rcu)Ken Helias
All other add functions for lists have the new item as first argument and the position where it is added as second argument. This was changed for no good reason in this function and makes using it unnecessary confusing. The name was changed to hlist_add_behind() to cause unconverted code to generate a compile error instead of using the wrong parameter order. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Ken Helias <kenhelias@firemail.de> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> [intel driver bits] Cc: Hugh Dickins <hughd@google.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-07-08documentation: Add pointer to percpu-ref for RCU and refcountPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
2014-07-08documentation: Update reference, kerneltrap.org no longer worksPranith Kumar
The kerneltrap.org site no longer works, so this commit updates it to a working reference, namely gmane. Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29documentation: Update API documentationPaul E. McKenney
This commit updates the list of RCU API members in whatisRCU.txt. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29documentation: Record rcu_dereference() value mishandlingPaul E. McKenney
Recent LKML discussings (see http://lwn.net/Articles/586838/ and http://lwn.net/Articles/588300/ for the LWN writeups) brought out some ways of misusing the return value from rcu_dereference() that are not necessarily completely intuitive. This commit therefore documents what can and cannot safely be done with these values. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2014-04-29documentation: Update sysfs path for rcu_cpu_stall_suppressPaul E. McKenney
Commit 6bfc09e2327d (rcu: Provide RCU CPU stall warnings for tiny RCU) moved the rcu_cpu_stall_suppress module parameter from rcutree.c to rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This commit therefore repairs this omission. Reported-by: Kirill Tkhai <tkhai@yandex.ru> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>