summaryrefslogtreecommitdiffstats
path: root/kernel/rcutree.c
Commit message (Collapse)AuthorAgeFilesLines
*---. Merge branches 'doctorture.2013.01.29a', 'fixes.2013.01.26a', ↵Paul E. McKenney2013-01-281-77/+183
|\ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'tagcb.2013.01.24a' and 'tiny.2013.01.29b' into HEAD doctorture.2013.01.11a: Changes to rcutorture and to RCU documentation. fixes.2013.01.26a: Miscellaneous fixes. tagcb.2013.01.24a: Tag RCU callbacks with grace-period number to simplify callback advancement. tiny.2013.01.29b: Enhancements to uniprocessor handling in tiny RCU.
| | | * rcu: Provide RCU CPU stall warnings for tiny RCUPaul E. McKenney2013-01-281-43/+3
| |_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tiny RCU has historically omitted RCU CPU stall warnings in order to reduce memory requirements, however, lack of these warnings caused Thomas Gleixner some debugging pain recently. Therefore, this commit adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory footprint small, while still enabling CPU stall warnings in kernels built to enable them. Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON config variable to simplify #if expressions. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * rcu: Trace callback accelerationPaul E. McKenney2013-01-081-0/+6
| | | | | | | | | | | | | | | | | | | | | This commit adds event tracing for callback acceleration to allow better tracking of callbacks through the system. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Tag callback lists with corresponding grace-period numberPaul E. McKenney2013-01-081-28/+167
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, callbacks are advanced each time the corresponding CPU notices a change in its leaf rcu_node structure's ->completed value (this value counts grace-period completions). This approach has worked quite well, but with the advent of RCU_FAST_NO_HZ, we cannot count on a given CPU seeing all the grace-period completions. When a CPU misses a grace-period completion that occurs while it is in dyntick-idle mode, this will delay invocation of its callbacks. In addition, acceleration of callbacks (when RCU realizes that a given callback need only wait until the end of the next grace period, rather than having to wait for a partial grace period followed by a full grace period) must be carried out extremely carefully. Insufficient acceleration will result in unnecessarily long grace-period latencies, while excessive acceleration will result in premature callback invocation. Changes that involve this tradeoff are therefore among the most nerve-wracking changes to RCU. This commit therefore explicitly tags groups of callbacks with the number of the grace period that they are waiting for. This means that callback-advancement and callback-acceleration functions are idempotent, so that excessive acceleration will merely waste a few CPU cycles. This also allows a CPU to take full advantage of any grace periods that have elapsed while it has been in dyntick-idle mode. It should also enable simulataneous simplifications to and optimizations of RCU_FAST_NO_HZ. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Remove unused code originally used for context trackingLi Zhong2013-01-261-3/+0
| | | | | | | | | | | | | | | | | | | | As context tracking subsystem evolved, it stopped using ignore_user_qs and in_user defined in the rcu_dynticks structure. This commit therefore removes them. Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
| * rcu: Correct 'optimized' to 'optimize' in header commentCody P Schafer2013-01-261-1/+1
| | | | | | | | | | | | | | | | | | Small grammar fix in rcutree comment regarding 'rcu_scheduler_active' var. Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| * rcu: Silence compiler array out-of-bounds false positivePaul E. McKenney2013-01-081-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It turns out that gcc 4.8 warns on array indexes being out of bounds unless it can prove otherwise. It gives this warning on some RCU initialization code. Because this is far from any fastpath, add an explicit check for array bounds and panic if so. This gives the compiler enough information to figure out that the array index is never out of bounds. However, if a similar false positive occurs on a fastpath, it will probably be necessary to tell the compiler to keep its array-index anxieties to itself. ;-) Markus Trippelsdorf <markus@trippelsdorf.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| * rcu: Use new nesting value for rcu_dyntick trace in rcu_eqs_enter_commonLi Zhong2013-01-081-1/+1
| | | | | | | | | | | | | | | | | | This patch uses the real new value of dynticks_nesting instead of 0 in rcu_eqs_enter_common(). Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| * rcu: Make rcu_is_cpu_rrupt_from_idle helper functions staticJosh Triplett2013-01-081-1/+1
|/ | | | | | | | | Both rcutiny and rcutree define a helper function named rcu_is_cpu_rrupt_from_idle(), each used exactly once, later in the same file. This commit therefore declares these helper functions static. Signed-off-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* context_tracking: New context tracking susbsystemFrederic Weisbecker2012-11-301-62/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Create a new subsystem that probes on kernel boundaries to keep track of the transitions between level contexts with two basic initial contexts: user or kernel. This is an abstraction of some RCU code that use such tracking to implement its userspace extended quiescent state. We need to pull this up from RCU into this new level of indirection because this tracking is also going to be used to implement an "on demand" generic virtual cputime accounting. A necessary step to shutdown the tick while still accounting the cputime. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Gilad Ben-Yossef <gilad@benyossef.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> [ paulmck: fix whitespace error and email address. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Add callback-free CPUsPaul E. McKenney2012-11-161-12/+51
| | | | | | | | | | | | | | | | | | | | | RCU callback execution can add significant OS jitter and also can degrade both scheduling latency and, in asymmetric multiprocessors, energy efficiency. This commit therefore adds the ability for selected CPUs ("rcu_nocbs=" boot parameter) to have their callbacks offloaded to kthreads. If the "rcu_nocb_poll" boot parameter is also specified, these kthreads will do polling, removing the need for the offloaded CPUs to do wakeups. At least one CPU must be doing normal callback processing: currently CPU 0 cannot be selected as a no-CBs CPU. In addition, attempts to offline the last normal-CBs CPU will fail. This feature was inspired by Jim Houston's and Joe Korty's JRCU, and this commit includes fixes to problems located by Fengguang Wu's kbuild test robot. [ paulmck: Added gfp.h include file as suggested by Fengguang Wu. ] Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*-----. Merge branches 'urgent.2012.10.27a', 'doc.2012.11.16a', 'fixes.2012.11.13a', ↵Paul E. McKenney2012-11-161-52/+170
|\ \ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'srcu.2012.10.27a', 'stall.2012.11.13a', 'tracing.2012.11.08a' and 'idle.2012.10.24a' into HEAD urgent.2012.10.27a: Fix for RCU user-mode transition (already in -tip). doc.2012.11.08a: Documentation updates, most notably codifying the memory-barrier guarantees inherent to grace periods. fixes.2012.11.13a: Miscellaneous fixes. srcu.2012.10.27a: Allow statically allocated and initialized srcu_struct structures (courtesy of Lai Jiangshan). stall.2012.11.13a: Add more diagnostic information to RCU CPU stall warnings, also decrease from 60 seconds to 21 seconds. hotplug.2012.11.08a: Minor updates to CPU hotplug handling. tracing.2012.11.08a: Improved debugfs tracing, courtesy of Michael Wang. idle.2012.10.24a: Updates to RCU idle/adaptive-idle handling, including a boot parameter that maps normal grace periods to expedited. Resolved conflict in kernel/rcutree.c due to side-by-side change.
| | | | * rcu: Fix precedence error in cpu_needs_another_gp()Paul E. McKenney2012-10-231-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The fix introduced by a10d206e (rcu: Fix day-one dyntick-idle stall-warning bug) has a C-language precedence error. It turns out that this error is harmless in that the same result is computed for all inputs, but the code is nevertheless a potential source of confusion. This commit therefore introduces parentheses in order to force the execution of the code to reflect the intent. Reported-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | | * rcu: Add a module parameter to force use of expedited RCU primitivesAntti P Miettinen2012-10-231-3/+9
| |_|_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There have been some embedded applications that would benefit from use of expedited grace-period primitives. In some ways, this is similar to synchronize_net() doing either a normal or an expedited grace period depending on lock state, but with control outside of the kernel. This commit therefore adds rcu_expedited boot and sysfs parameters that cause the kernel to substitute expedited primitives for the normal grace-period primitives. [ paulmck: Add trace/event/rcu.h to kernel/srcu.c to avoid build error. Get rid of infinite loop through contention path.] Signed-off-by: Antti P Miettinen <amiettinen@nvidia.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Fix tracing formattingPaul E. McKenney2012-11-081-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_state structure's ->completed field is unsigned long, so this commit adjusts show_one_rcugp()'s printf() format to suit. Also add the required ACCESS_ONCE() directives while we are in this function. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Instrument synchronize_rcu_expedited() for debugfs tracingPaul E. McKenney2012-11-081-3/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit adds the counters to rcu_state and updates them in synchronize_rcu_expedited() to provide the data needed for debugfs tracing. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Move synchronize_sched_expedited() state to rcu_statePaul E. McKenney2012-11-081-11/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tracing (debugfs) of expedited RCU primitives is required, which in turn requires that the relevant data be located where the tracing code can find it, not in its current static global variables in kernel/rcutree.c. This commit therefore moves sync_sched_expedited_started and sync_sched_expedited_done to the rcu_state structure, as fields ->expedited_start and ->expedited_done, respectively. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Avoid counter wrap in synchronize_sched_expedited()Paul E. McKenney2012-11-081-18/+44
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There is a counter scheme similar to ticket locking that synchronize_sched_expedited() uses to service multiple concurrent callers with the same expedited grace period. Upon entry, a sync_sched_expedited_started variable is atomically incremented, and upon completion of a expedited grace period a separate sync_sched_expedited_done variable is atomically incremented. However, if a synchronize_sched_expedited() is delayed while in try_stop_cpus(), concurrent invocations will increment the sync_sched_expedited_started counter, which will eventually overflow. If the original synchronize_sched_expedited() resumes execution just as the counter overflows, a concurrent invocation could incorrectly conclude that an expedited grace period elapsed in zero time, which would be bad. One could rely on counter size to prevent this from happening in practice, but the goal is to formally validate this code, so it needs to be fixed anyway. This commit therefore checks the gap between the two counters before incrementing sync_sched_expedited_started, and if the gap is too large, does a normal grace period instead. Overflow is thus only possible if there are more than about 3.5 billion threads on 32-bit systems, which can be excluded until such time as task_struct fits into a single byte and 4G/4G patches are accepted into mainline. It is also easy to encode this limitation into mechanical theorem provers. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Rename ->onofflock to ->orphan_lockPaul E. McKenney2012-11-081-6/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The ->onofflock field in the rcu_state structure at one time synchronized CPU-hotplug operations for RCU. However, its scope has decreased over time so that it now only protects the lists of orphaned RCU callbacks. This commit therefore renames it to ->orphan_lock to reflect its current use. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | | * rcu: Fix comment about _rcu_barrier()/orphanage exclusionPaul E. McKenney2012-10-231-2/+2
| |_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In the old days, _rcu_barrier() acquired ->onofflock to exclude rcu_send_cbs_to_orphanage(), which allowed the latter to avoid memory barriers in callback handling. However, _rcu_barrier() recently started doing get_online_cpus() to lock out CPU-hotplug operations entirely, which means that the comment in rcu_send_cbs_to_orphanage() that talks about ->onofflock is now obsolete. This commit therefore fixes the comment. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Dump number of callbacks in stall warning messagesPaul E. McKenney2012-10-231-4/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In theory, if a grace period manages to get started despite there being no callbacks on any of the CPUs, all CPUs could go into dyntick-idle mode, so that the grace period would never end. This commit updates the RCU CPU stall warning messages to detect this condition by summing up the number of callbacks on all CPUs. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Add grace-period information to RCU CPU stall warningsPaul E. McKenney2012-10-231-3/+5
| | | | | | | | | | | | | | | | | | | | | | | | This commit causes the last grace period started and completed to be printed on RCU CPU stall warning messages in order to aid diagnosis. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * rcu: Print remote CPU's stacks in stall warningsPaul E. McKenney2012-10-231-1/+24
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | The RCU CPU stall warnings rely on trigger_all_cpu_backtrace() to do NMI-based dump of the stack traces of all CPUs. Unfortunately, a number of architectures do not implement trigger_all_cpu_backtrace(), in which case RCU falls back to just dumping the stack of the running CPU. This is unhelpful in the case where the running CPU has detected that some other CPU has stalled. This commit therefore makes the running CPU dump the stacks of the tasks running on the stalled CPUs. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| * rcu: Clarify memory-ordering properties of grace-period primitivesPaul E. McKenney2012-11-131-4/+25
| | | | | | | | | | | | | | | | | | | | | | | | This commit explicitly states the memory-ordering properties of the RCU grace-period primitives. Although these properties were in some sense implied by the fundmental property of RCU ("a grace period must wait for all pre-existing RCU read-side critical sections to complete"), stating it explicitly will be a great labor-saving device. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
| * rcu: Fix batch-limit size problemEric Dumazet2012-11-131-7/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 29c00b4a1d9e27 (rcu: Add event-tracing for RCU callback invocation) added a regression in rcu_do_batch() Under stress, RCU is supposed to allow to process all items in queue, instead of a batch of 10 items (blimit), but an integer overflow makes the effective limit being 1. So, unless there is frequent idle periods (during which RCU ignores batch limits), RCU can be forced into a state where it cannot keep up with the callback-generation rate, eventually resulting in OOM. This commit therefore converts a few variables in rcu_do_batch() from int to long to fix this problem, along with the module parameters controlling the batch limits. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: <stable@vger.kernel.org> # 3.2 +
| * rcu: Accelerate callbacks for CPU initiating a grace periodPaul E. McKenney2012-10-201-2/+24
|/ | | | | | | | | | | | | | | Because grace-period initialization is carried out by a separate kthread, it might happen on a different CPU than the one that had the callback needing a grace period -- which is where the callback acceleration needs to happen. Fortunately, rcu_start_gp() holds the root rcu_node structure's ->lock, which prevents a new grace period from starting. This allows this function to safely determine that a grace period has not yet started, which in turn allows it to fully accelerate any callbacks that it has pending. This commit adds this acceleration. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* rcu: Grace-period initialization excludes only RCU notifierPaul E. McKenney2012-10-081-11/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Kirill noted the following deadlock cycle on shutdown involving padata: > With commit 755609a9087fa983f567dc5452b2fa7b089b591f I've got deadlock on > poweroff. > > It guess it happens because of race for cpu_hotplug.lock: > > CPU A CPU B > disable_nonboot_cpus() > _cpu_down() > cpu_hotplug_begin() > mutex_lock(&cpu_hotplug.lock); > __cpu_notify() > padata_cpu_callback() > __padata_remove_cpu() > padata_replace() > synchronize_rcu() > rcu_gp_kthread() > get_online_cpus(); > mutex_lock(&cpu_hotplug.lock); It would of course be good to eliminate grace-period delays from CPU-hotplug notifiers, but that is a separate issue. Deadlock is not an appropriate diagnostic for excessive CPU-hotplug latency. Fortunately, grace-period initialization does not actually need to exclude all of the CPU-hotplug operation, but rather only RCU's own CPU_UP_PREPARE and CPU_DEAD CPU-hotplug notifiers. This commit therefore introduces a new per-rcu_state onoff_mutex that provides the required concurrency control in place of the get_online_cpus() that was previously in rcu_gp_init(). Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Kirill A. Shutemov <kirill@shutemov.name>
* rcu: Apply micro-optimization and int/bool fixes to RCU's idle handlingPaul E. McKenney2012-09-261-8/+8
| | | | | | | | | | | | Checking "user" before "is_idle_task()" allows better optimizations in cases where inlining is possible. Also, "bool" should be passed "true" or "false" rather than "1" or "0". This commit therefore makes these changes, as noted in Josh's review. Reported-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Userspace RCU extended QS selftestFrederic Weisbecker2012-09-261-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Provide a config option that enables the userspace RCU extended quiescent state on every CPUs by default. This is for testing purpose. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Switch task's syscall hooks on context switchFrederic Weisbecker2012-09-261-0/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Clear the syscalls hook of a task when it's scheduled out so that if the task migrates, it doesn't run the syscall slow path on a CPU that might not need it. Also set the syscalls hook on the next task if needed. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Ignore userspace extended quiescent state by defaultFrederic Weisbecker2012-09-261-1/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | By default we don't want to enter into RCU extended quiescent state while in userspace because doing this produces some overhead (eg: use of syscall slowpath). Set it off by default and ready to run when some feature like adaptive tickless need it. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Allow rcu_user_enter()/exit() to nestFrederic Weisbecker2012-09-261-8/+33
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Allow calls to rcu_user_enter() even if we are already in userspace (as seen by RCU) and allow calls to rcu_user_exit() even if we are already in the kernel. This makes the APIs more flexible to be called from architectures. Exception entries for example won't need to know if they come from userspace before calling rcu_user_exit(). Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: Settle config for userspace extended quiescent stateFrederic Weisbecker2012-09-261-1/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Create a new config option under the RCU menu that put CPUs under RCU extended quiescent state (as in dynticks idle mode) when they run in userspace. This require some contribution from architectures to hook into kernel and userspace boundaries. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIsFrederic Weisbecker2012-09-261-0/+43
| | | | | | | | | | | | | | | | | | | | | | | | | | | | In some cases, it is necessary to enter or exit userspace-RCU-idle mode from an interrupt handler, for example, if some other CPU sends this CPU a resched IPI. In this case, the current CPU would enter the IPI handler in userspace-RCU-idle mode, but would need to exit the IPI handler after having exited that mode. To allow this to work, this commit adds two new APIs to TREE_RCU: - rcu_user_enter_after_irq(). This must be called from an interrupt between rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(), the irq handler will return into an RCU extended quiescent state. In theory, this interrupt is never a nested interrupt, but in practice it might interrupt softirq, which looks to RCU like a nested interrupt. - rcu_user_exit_after_irq(). This must be called from a non-nesting interrupt, interrupting an RCU extended quiescent state, also between rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(), the irq handler will return in an RCU non-quiescent state. [ Combined with "Allow calls to rcu_exit_user_irq from nesting irqs." ] Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* rcu: New rcu_user_enter() and rcu_user_exit() APIsFrederic Weisbecker2012-09-261-34/+101
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | RCU currently insists that only idle tasks can enter RCU idle mode, which prohibits an adaptive tickless kernel (AKA nohz cpusets), which in turn would mean that usermode execution would always take scheduling-clock interrupts, even when there is only one task runnable on the CPU in question. This commit therefore adds rcu_user_enter() and rcu_user_exit(), which allow non-idle tasks to enter RCU idle mode. These are quite similar to rcu_idle_enter() and rcu_idle_exit(), respectively, except that they omit the idle-task checks. [ Updated to use "user" flag rather than separate check functions. ] [ paulmck: Updated to drop exports of new functions based on Josh's patch getting rid of the need for them. ] Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Alessio Igor Bogani <abogani@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Avi Kivity <avi@redhat.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@ti.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <shemminger@vyatta.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* Merge remote-tracking branch 'tip/smp/hotplug' into next.2012.09.25bPaul E. McKenney2012-09-251-8/+4
|\ | | | | | | | | | | The conflicts between kernel/rcutree.h and kernel/rcutree_plugin.h were due to adjacent insertions and deletions, which were resolved by simply accepting the changes on both branches.
| * rcu: Use smp_hotplug_thread facility for RCUs per-CPU kthreadPaul E. McKenney2012-08-131-4/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Bring RCU into the new-age CPU-hotplug fold by modifying RCU's per-CPU kthread code to use the new smp_hotplug_thread facility. [ tglx: Adapted it to use callbacks and to the simplified rcu yield ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Namhyung Kim <namhyung@kernel.org> Link: http://lkml.kernel.org/r/20120716103948.673354828@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| * rcu: Yield simplerThomas Gleixner2012-08-131-4/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_yield() code is amazing. It's there to avoid starvation of the system when lots of (boosting) work is to be done. Now looking at the code it's functionality is: Make the thread SCHED_OTHER and very nice, i.e. get it out of the way Arm a timer with 2 ticks schedule() Now if the system goes idle the rcu task returns, regains SCHED_FIFO and plugs on. If the systems stays busy the timer fires and wakes a per node kthread which in turn makes the per cpu thread SCHED_FIFO and brings it back on the cpu. For the boosting thread the "make it FIFO" bit is missing and it just runs some magic boost checks. Now this is a lot of code with extra threads and complexity. It's way simpler to let the tasks when they detect overload schedule away for 2 ticks and defer the normal wakeup as long as they are in yielded state and the cpu is not idle. That solves the same problem and the only difference is that when the cpu goes idle it's not guaranteed that the thread returns right away, but it won't be longer out than two ticks, so no harm is done. If that's an issue than it is way simpler just to wake the task from idle as RCU has callbacks there anyway. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Namhyung Kim <namhyung@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20120716103948.131256723@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
| |
| \
| \
| \
*---. \ Merge branches 'bigrt.2012.09.23a', 'doctorture.2012.09.23a', ↵Paul E. McKenney2012-09-241-114/+52
|\ \ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'fixes.2012.09.23a', 'hotplug.2012.09.23a' and 'idlechop.2012.09.23a' into HEAD bigrt.2012.09.23a contains additional commits to reduce scheduling latency from RCU on huge systems (many hundrends or thousands of CPUs). doctorture.2012.09.23a contains documentation changes and rcutorture fixes. fixes.2012.09.23a contains miscellaneous fixes. hotplug.2012.09.23a contains CPU-hotplug-related changes. idle.2012.09.23a fixes architectures for which RCU no longer considered the idle loop to be a quiescent state due to earlier adaptive-dynticks changes. Affected architectures are alpha, cris, frv, h8300, m32r, m68k, mn10300, parisc, score, xtensa, and ia64.
| | | * | rcu: Disallow callback registry on offline CPUsPaul E. McKenney2012-09-231-0/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Posting a callback after the CPU_DEAD notifier effectively leaks that callback unless/until that CPU comes back online. Silence is unhelpful when attempting to track down such leaks, so this commit emits a WARN_ON_ONCE() and unconditionally leaks the callback when an offline CPU attempts to register a callback. The rdp->nxttail[RCU_NEXT_TAIL] is set to NULL in the CPU_DEAD notifier and restored in the CPU_UP_PREPARE notifier, allowing _call_rcu() to determine exactly when posting callbacks is illegal. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | | * | rcu: Remove _rcu_barrier() dependency on __stop_machine()Paul E. McKenney2012-09-231-72/+11
| | |/ / | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, _rcu_barrier() relies on preempt_disable() to prevent any CPU from going offline, which in turn depends on CPU hotplug's use of __stop_machine(). This patch therefore makes _rcu_barrier() use get_online_cpus() to block CPU-hotplug operations. This has the added benefit of removing the need for _rcu_barrier() to adopt callbacks: Because CPU-hotplug operations are excluded, there can be no callbacks to adopt. This commit simplifies the code accordingly. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * | rcu: Remove redundant memory barrier from __call_rcu()Paul E. McKenney2012-09-231-2/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The first memory barrier in __call_rcu() is supposed to order any updates done beforehand by the caller against the actual queuing of the callback. However, the second memory barrier (which is intended to order incrementing the queue lengths before queuing the callback) is also between the caller's updates and the queuing of the callback. The second memory barrier can therefore serve both purposes. This commit therefore removes the first memory barrier. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * | rcu: Avoid spurious RCU CPU stall warningsPaul E. McKenney2012-09-231-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If a given CPU avoids the idle loop but also avoids starting a new RCU grace period for a full minute, RCU can issue spurious RCU CPU stall warnings. This commit fixes this issue by adding a check for ongoing grace period to avoid these spurious stall warnings. Reported-by: Becky Bruce <bgillbruce@gmail.com> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| | * | rcu: Protect rcu_node accesses during CPU stall warningsPaul E. McKenney2012-09-231-7/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The print_other_cpu_stall() function accesses a number of rcu_node fields without protection from the ->lock. In theory, this is not a problem because the fields accessed are all integers, but in practice the compiler can get nasty. Therefore, the commit extends the existing critical section to cover the entire loop body. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| | * | rcu: Make offline-CPU checking allow for indefinite delaysPaul E. McKenney2012-09-231-32/+21
| |/ / | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_implicit_offline_qs() function implicitly assumed that execution would progress predictably when interrupts are disabled, which is of course not guaranteed when running on a hypervisor. Furthermore, this function is short, and is called from one place only in a short function. This commit therefore ensures that the timing is checked before checking the condition, which guarantees correct behavior even given indefinite delays. It also inlines rcu_implicit_offline_qs() into rcu_implicit_dynticks_qs(). Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* | | rcu: Shrink RCU based on number of CPUsPaul E. McKenney2012-09-231-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, rcu_init_geometry() only reshapes RCU's combining trees if the leaf fanout is changed at boot time. This means that by default, kernels compiled with (say) NR_CPUS=4096 will keep oversized data structures, even when running on systems with (say) four CPUs. This commit therefore checks to see if the maximum number of CPUs on the actual running system (nr_cpu_ids) differs from NR_CPUS, and if so reshapes the combining trees accordingly. Reported-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | | rcu: Handle unbalanced rcu_node configurations with few CPUsPaul E. McKenney2012-09-231-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If CONFIG_RCU_FANOUT_EXACT=y, if there are not enough CPUs (according to nr_cpu_ids) to require more than a single rcu_node structure, but if NR_CPUS is larger than would fit into a single rcu_node structure, then the current rcu_init_levelspread() code is subject to integer overflow in the eight-bit ->levelspread[] array in the rcu_state structure. In this case, the solution is -not- to increase the size of the elements in this array because the values in that array should be constrained to the number of bits in an unsigned long. Instead, this commit replaces NR_CPUS with nr_cpu_ids in the rcu_init_levelspread() function's initialization of the cprv local variable. This results in all of the arithmetic being consistently based off of the nr_cpu_ids value, thus avoiding the overflow, which was caused by the mixing of nr_cpu_ids and NR_CPUS. Reported-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
* | | rcu: Simplify quiescent-state detectionPaul E. McKenney2012-09-231-16/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current quiescent-state detection algorithm is needlessly complex. It records the grace-period number corresponding to the quiescent state at the time of the quiescent state, which works, but it seems better to simply erase any record of previous quiescent states at the time that the CPU notices the new grace period. This has the further advantage of removing another piece of RCU for which lockless reasoning is required. Therefore, this commit makes this change. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* | | rcu: Adjust for unconditional ->completed assignmentPaul E. McKenney2012-09-231-1/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Now that the rcu_node structures' ->completed fields are unconditionally assigned at grace-period cleanup time, they should already have the correct value for the new grace period at grace-period initialization time. This commit therefore inserts a WARN_ON_ONCE() to verify this invariant. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
* | | rcu: Add random PROVE_RCU_DELAY to grace-period initializationPaul E. McKenney2012-09-231-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | Preemption greatly raised the probability of certain types of race conditions, so this commit adds an anti-heisenbug to greatly increase the collision cross section, also known as the probability of occurrence. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
OpenPOWER on IntegriCloud