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2020-06-07Merge tag 'tty-5.8-rc1' of ↵Linus Torvalds1-1/+1
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty Pull tty/serial driver updates from Greg KH: "Here is the tty and serial driver updates for 5.8-rc1 Nothing huge at all, just a lot of little serial driver fixes, updates for new devices and features, and other small things. Full details are in the shortlog. All of these have been in linux-next with no issues for a while" * tag 'tty-5.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (67 commits) tty: serial: qcom_geni_serial: Add 51.2MHz frequency support tty: serial: imx: clear Ageing Timer Interrupt in handler serial: 8250_fintek: Add F81966 Support sc16is7xx: Add flag to activate IrDA mode dt-bindings: sc16is7xx: Add flag to activate IrDA mode serial: 8250: Support rs485 bus termination GPIO serial: 8520_port: Fix function param documentation dt-bindings: serial: Add binding for rs485 bus termination GPIO vt: keyboard: avoid signed integer overflow in k_ascii serial: 8250: Enable 16550A variants by default on non-x86 tty: hvc_console, fix crashes on parallel open/close serial: imx: Initialize lock for non-registered console sc16is7xx: Read the LSR register for basic device presence check sc16is7xx: Allow sharing the IRQ line sc16is7xx: Use threaded IRQ sc16is7xx: Always use falling edge IRQ tty: n_gsm: Fix bogus i++ in gsm_data_kick tty: n_gsm: Remove unnecessary test in gsm_print_packet() serial: stm32: add no_console_suspend support tty: serial: fsl_lpuart: Use __maybe_unused instead of #if CONFIG_PM_SLEEP ...
2020-06-01Merge branch 'WIP.core/rcu' into core/rcu, to pick up two x86/entry dependenciesIngo Molnar1-20/+80
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2020-05-28rcu: Allow for smp_call_function() running callbacks from idlePeter Zijlstra1-6/+19
Current RCU hard relies on smp_call_function() callbacks running from interrupt context. A pending optimization is going to break that, it will allow idle CPUs to run the callbacks from the idle loop. This avoids raising the IPI on the requesting CPU and avoids handling an exception on the receiving CPU. Change rcu_is_cpu_rrupt_from_idle() to also accept task context, provided it is the idle task. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Link: https://lore.kernel.org/r/20200527171236.GC706495@hirez.programming.kicks-ass.net
2020-05-26rcu: Provide rcu_irq_exit_check_preempt()Thomas Gleixner1-0/+18
Provide a debug check which can be invoked from exception return to kernel mode before an attempt is made to schedule. Warn if RCU is not ready for this. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20200521202117.089709607@linutronix.de
2020-05-26rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()Paul E. McKenney1-20/+62
There will likely be exception handlers that can sleep, which rules out the usual approach of invoking rcu_nmi_enter() on entry and also rcu_nmi_exit() on all exit paths. However, the alternative approach of just not calling anything can prevent RCU from coaxing quiescent states from nohz_full CPUs that are looping in the kernel: RCU must instead IPI them explicitly. It would be better to enable the scheduler tick on such CPUs to interact with RCU in a lighter-weight manner, and this enabling is one of the things that rcu_nmi_enter() currently does. What is needed is something that helps RCU coax quiescent states while not preventing subsequent sleeps. This commit therefore splits out the nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter() logic into a new function named rcu_irq_enter_check_tick(). [ tglx: Renamed the function and made it a nop when context tracking is off ] [ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ] Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de
2020-05-19rcu: Provide __rcu_is_watching()Thomas Gleixner1-0/+5
Same as rcu_is_watching() but without the preempt_disable/enable() pair inside the function. It is merked noinstr so it ends up in the non-instrumentable text section. This is useful for non-preemptible code especially in the low level entry section. Using rcu_is_watching() there results in a call to the preempt_schedule_notrace() thunk which triggers noinstr section warnings in objtool. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200512213810.518709291@linutronix.de
2020-05-19rcu: Provide rcu_irq_exit_preempt()Thomas Gleixner1-0/+22
Interrupts and exceptions invoke rcu_irq_enter() on entry and need to invoke rcu_irq_exit() before they either return to the interrupted code or invoke the scheduler due to preemption. The general assumption is that RCU idle code has to have preemption disabled so that a return from interrupt cannot schedule. So the return from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq(). If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code had preemption enabled then this goes unnoticed until the CPU goes idle or some other RCU check is executed. Provide rcu_irq_exit_preempt() which can be invoked from the interrupt/exception return code in case that preemption is enabled. It invokes rcu_irq_exit() and contains a few sanity checks in case that CONFIG_PROVE_RCU is enabled to catch such issues directly. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200505134904.364456424@linutronix.de
2020-05-19rcu: Make RCU IRQ enter/exit functions rely on in_nmi()Paul E. McKenney1-32/+15
The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an "irq" parameter that indicates whether these functions have been invoked from an irq handler (irq==true) or an NMI handler (irq==false). However, recent changes have applied notrace to a few critical functions such that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely on in_nmi(). Note that in_nmi() works no differently than before, but rather that tracing is now prohibited in code regions where in_nmi() would incorrectly report NMI state. Therefore remove the "irq" parameter and inline rcu_nmi_enter_common() and rcu_nmi_exit_common() into rcu_nmi_enter() and rcu_nmi_exit(), respectively. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> Link: https://lkml.kernel.org/r/20200505134101.617130349@linutronix.de
2020-05-19rcu/tree: Mark the idle relevant functions noinstrThomas Gleixner3-41/+49
These functions are invoked from context tracking and other places in the low level entry code. Move them into the .noinstr.text section to exclude them from instrumentation. Mark the places which are safe to invoke traceable functions with instrumentation_begin/end() so objtool won't complain. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Paul E. McKenney <paulmck@kernel.org> Link: https://lkml.kernel.org/r/20200505134100.575356107@linutronix.de
2020-05-15rcu: constify sysrq_key_opEmil Velikov1-1/+1
With earlier commits, the API no longer discards the const-ness of the sysrq_key_op. As such we can add the notation. Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.com> Cc: linux-kernel@vger.kernel.org Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: rcu@vger.kernel.org Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com> Link: https://lore.kernel.org/r/20200513214351.2138580-11-emil.l.velikov@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-05-07Merge branches 'fixes.2020.04.27a', 'kfree_rcu.2020.04.27a', ↵Paul E. McKenney12-465/+1669
'rcu-tasks.2020.04.27a', 'stall.2020.04.27a' and 'torture.2020.05.07a' into HEAD fixes.2020.04.27a: Miscellaneous fixes. kfree_rcu.2020.04.27a: Changes related to kfree_rcu(). rcu-tasks.2020.04.27a: Addition of new RCU-tasks flavors. stall.2020.04.27a: RCU CPU stall-warning updates. torture.2020.05.07a: Torture-test updates.
2020-05-07rcutorture: Convert ULONG_CMP_LT() to time_before()Paul E. McKenney1-3/+3
This commit converts three ULONG_CMP_LT() invocations in rcutorture to time_before() to reflect the fact that they are comparing timestamps to the jiffies counter. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-05-07rcutorture: Make rcu_fwds and rcu_fwd_emergency_stop staticJason Yan1-2/+2
This commit fixes the following sparse warning: kernel/rcu/rcutorture.c:1695:16: warning: symbol 'rcu_fwds' was not declared. Should it be static? kernel/rcu/rcutorture.c:1696:6: warning: symbol 'rcu_fwd_emergency_stop' was not declared. Should it be static? Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: Jason Yan <yanaijie@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-05-07rcu: Allow rcutorture to starve grace-period kthreadPaul E. McKenney3-3/+44
This commit provides an rcutorture.stall_gp_kthread module parameter to allow rcutorture to starve the grace-period kthread. This allows testing the code that detects such starvation. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-05-07rcutorture: Add flag to produce non-busy-wait task stallsPaul E. McKenney1-6/+11
This commit aids testing of RCU task stall warning messages by adding an rcutorture.stall_cpu_block module parameter that results in the induced stall sleeping within the RCU read-side critical section. Spinning with interrupts disabled is still available via the rcutorture.stall_cpu_irqsoff module parameter, and specifying neither of these two module parameters will spin with preemption disabled. Note that sleeping (as opposed to preemption) results in additional complaints from RCU at context-switch time, so yet more testing. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcutorture: Mark data-race potential for rcu_barrier() test statisticsPaul E. McKenney1-3/+3
The n_barrier_successes, n_barrier_attempts, and n_rcu_torture_barrier_error variables are updated (without access markings) by the main rcu_barrier() test kthread, and accessed (also without access markings) by the rcu_torture_stats() kthread. This of course can result in KCSAN complaints. Because the accesses are in diagnostic prints, this commit uses data_race() to excuse the diagnostic prints from the data race. If this were to ever cause bogus statistics prints (for example, due to store tearing), any misleading information would be disambiguated by the presence or absence of an rcutorture splat. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely and due to the mild consequences of the failure, namely a confusing rcutorture console message. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
2020-04-27rcutorture: Add KCSAN stubsPaul E. McKenney1-0/+12
This commit adds stubs for KCSAN's data_race(), ASSERT_EXCLUSIVE_WRITER(), and ASSERT_EXCLUSIVE_ACCESS() macros to allow code using these macros to move ahead. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu: Remove self-stack-trace when all quiescent states seenPaul E. McKenney1-2/+0
When all quiescent states have been seen, it is normally the grace-period kthread that is in trouble. Although the existing stack trace from the current CPU might possibly provide useful information, experience indicates that there is too much noise for this to be worthwhile. This commit therefore removes this stack trace from the output. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu: When GP kthread is starved, tag idle threads as false positivesPaul E. McKenney1-5/+19
If the grace-period kthread is starved, idle threads' extended quiescent states are not reported. These idle threads thus wrongly appear to be blocking the current grace period. This commit therefore tags such idle threads as probable false positives when the grace-period kthread is being starved. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu: Use data_race() for RCU expedited CPU stall-warning printsPaul E. McKenney1-4/+4
Although the accesses used to determine whether or not an expedited stall should be printed are an integral part of the concurrency algorithm governing use of the corresponding variables, the values that are simply printed are ancillary. As such, it is best to use data_race() for these accesses in order to provide the greatest latitude in the use of KCSAN for the other accesses that are an integral part of the algorithm. This commit therefore changes the relevant uses of READ_ONCE() to data_race(). Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Allow standalone use of TASKS_{TRACE_,}RCUPaul E. McKenney1-24/+30
This commit allows TASKS_TRACE_RCU to be used independently of TASKS_RCU and vice versa. [ paulmck: Fix conditional compilation per kbuild test robot feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add IPI failure count to statisticsPaul E. McKenney1-4/+7
This commit adds a failure-return count for smp_call_function_single(), and adds this to the console messages for rcutorture writer stalls and at the end of rcutorture testing. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add count for idle tasks on offline CPUsPaul E. McKenney1-1/+5
This commit adds a counter for the number of times the quiescent state was an idle task associated with an offline CPU, and prints this count at the end of rcutorture runs and at stall time. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add rcu_dynticks_zero_in_eqs() effectiveness statisticsPaul E. McKenney1-2/+11
This commit adds counts of the number of calls and number of successful calls to rcu_dynticks_zero_in_eqs(), which are printed at the end of rcutorture runs and at stall time. This allows evaluation of the effectiveness of rcu_dynticks_zero_in_eqs(). Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Make RCU tasks trace also wait for idle tasksPaul E. McKenney1-5/+13
This commit scans the CPUs, adding each CPU's idle task to the list of tasks that need quiescent states. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Handle the running-offline idle-task special casePaul E. McKenney1-2/+6
The idle task corresponding to an offline CPU can appear to be running while that CPU is offline. This commit therefore adds checks for this situation, treating it as a quiescent state. Because the tasklist scan and the holdout-list scan now exclude CPU-hotplug operations, readers on the CPU-hotplug paths are still waited for. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Disable CPU hotplug across RCU tasks trace scansPaul E. McKenney1-4/+14
This commit disables CPU hotplug across RCU tasks trace scans, which is a first step towards correctly recognizing idle tasks "running" on offline CPUs. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Allow rcu_read_unlock_trace() under scheduler locksPaul E. McKenney2-1/+12
The rcu_read_unlock_trace() can invoke rcu_read_unlock_trace_special(), which in turn can call wake_up(). Therefore, if any scheduler lock is held across a call to rcu_read_unlock_trace(), self-deadlock can occur. This commit therefore uses the irq_work facility to defer the wake_up() to a clean environment where no scheduler locks will be held. Reported-by: Steven Rostedt <rostedt@goodmis.org> [ paulmck: Update #includes for m68k per kbuild test robot. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Avoid IPIing userspace/idle tasks if kernel is so builtPaul E. McKenney5-10/+72
Systems running CPU-bound real-time task do not want IPIs sent to CPUs executing nohz_full userspace tasks. Battery-powered systems don't want IPIs sent to idle CPUs in low-power mode. Unfortunately, RCU tasks trace can and will send such IPIs in some cases. Both of these situations occur only when the target CPU is in RCU dyntick-idle mode, in other words, when RCU is not watching the target CPU. This suggests that CPUs in dyntick-idle mode should use memory barriers in outermost invocations of rcu_read_lock_trace() and rcu_read_unlock_trace(), which would allow the RCU tasks trace grace period to directly read out the target CPU's read-side state. One challenge is that RCU tasks trace is not targeting a specific CPU, but rather a task. And that task could switch from one CPU to another at any time. This commit therefore uses try_invoke_on_locked_down_task() and checks for task_curr() in trc_inspect_reader_notrunning(). When this condition holds, the target task is running and cannot move. If CONFIG_TASKS_TRACE_RCU_READ_MB=y, the new rcu_dynticks_zero_in_eqs() function can be used to check if the specified integer (in this case, t->trc_reader_nesting) is zero while the target CPU remains in that same dyntick-idle sojourn. If so, the target task is in a quiescent state. If not, trc_read_check_handler() must indicate failure so that the grace-period kthread can take appropriate action or retry after an appropriate delay, as the case may be. With this change, given CONFIG_TASKS_TRACE_RCU_READ_MB=y, if a given CPU remains idle or a given task continues executing in nohz_full mode, the RCU tasks trace grace-period kthread will detect this without the need to send an IPI. Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add Kconfig option to mediate smp_mb() vs. IPIPaul E. McKenney2-1/+20
This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that enables use of read-side memory barriers by both rcu_read_lock_trace() and rcu_read_unlock_trace() when the are executed with the current->trc_reader_special.b.need_mb flag set. This flag is currently never set. Doing that is the subject of a later commit. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add grace-period and IPI counts to statisticsPaul E. McKenney1-1/+9
This commit adds a grace-period count and a count of IPIs sent since boot, which is printed in response to rcutorture writer stalls and at the end of rcutorture testing. These counts will be used to evaluate various schemes to reduce the number of IPIs sent. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Split ->trc_reader_need_endPaul E. McKenney1-13/+20
This commit splits ->trc_reader_need_end by using the rcu_special union. This change permits readers to check to see if a memory barrier is required without any added overhead in the common case where no such barrier is required. This commit also adds the read-side checking. Later commits will add the machinery to properly set the new ->trc_reader_special.b.need_mb field. This commit also makes rcu_read_unlock_trace_special() tolerate nested read-side critical sections within interrupt and NMI handlers. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Provide boot parameter to delay IPIs until late in grace periodPaul E. McKenney1-4/+9
This commit provides a rcupdate.rcu_task_ipi_delay kernel boot parameter that specifies how old the RCU tasks trace grace period must be before the grace-period kthread starts sending IPIs. This delay allows more tasks to pass through rcu_tasks_qs() quiescent states, thus reducing (or even eliminating) the number of IPIs that must be sent. On a short rcutorture test setting this kernel boot parameter to HZ/2 resulted in zero IPIs for all 877 RCU-tasks trace grace periods that elapsed during that test. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add a grace-period start time for throttling and debugPaul E. McKenney1-0/+2
This commit adds a place to record the grace-period start in jiffies. This will be used by later commits for debugging purposes and to throttle IPIs early in the grace period. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Make RCU Tasks Trace make use of RCU scheduler hooksPaul E. McKenney2-6/+5
This commit makes the calls to rcu_tasks_qs() detect and report quiescent states for RCU tasks trace. If the task is in a quiescent state and if ->trc_reader_checked is not yet set, the task sets its own ->trc_reader_checked. This will cause the grace-period kthread to remove it from the holdout list if it still remains there. [ paulmck: Fix conditional compilation per kbuild test robot feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Make rcutorture writer stall output include GP statePaul E. McKenney1-5/+72
This commit adds grace-period state and time to the rcutorture writer stall output. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add RCU tasks to rcutorture writer stall outputPaul E. McKenney3-3/+45
This commit adds state for each RCU-tasks flavor to the rcutorture writer stall output. The initial state is minimal, but you have to start somewhere. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> [ paulmck: Fixes based on feedback from kbuild test robot. ]
2020-04-27rcu-tasks: Move #ifdef into tasks.hPaul E. McKenney2-4/+5
This commit pushes the #ifdef CONFIG_TASKS_RCU_GENERIC from kernel/rcu/update.c to kernel/rcu/tasks.h in order to improve readability as more APIs are added. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add stall warnings for RCU Tasks TracePaul E. McKenney1-4/+66
This commit adds RCU CPU stall warnings for RCU Tasks Trace. These dump out any tasks blocking the current grace period, as well as any CPUs that have not responded to an IPI request. This happens in two phases, when initially extracting state from the tasks and later when waiting for any holdout tasks to check in. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcutorture: Add torture tests for RCU Tasks TracePaul E. McKenney3-1/+46
This commit adds the definitions required to torture the tracing flavor of RCU tasks. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add an RCU Tasks Trace to simplify protection of tracing hooksPaul E. McKenney2-5/+367
Because RCU does not watch exception early-entry/late-exit, idle-loop, or CPU-hotplug execution, protection of tracing and BPF operations is needlessly complicated. This commit therefore adds a variant of Tasks RCU that: o Has explicit read-side markers to allow finite grace periods in the face of in-kernel loops for PREEMPT=n builds. These markers are rcu_read_lock_trace() and rcu_read_unlock_trace(). o Protects code in the idle loop, exception entry/exit, and CPU-hotplug code paths. In this respect, RCU-tasks trace is similar to SRCU, but with lighter-weight readers. o Avoids expensive read-side instruction, having overhead similar to that of Preemptible RCU. There are of course downsides: o The grace-period code can send IPIs to CPUs, even when those CPUs are in the idle loop or in nohz_full userspace. This is mitigated by later commits. o It is necessary to scan the full tasklist, much as for Tasks RCU. o There is a single callback queue guarded by a single lock, again, much as for Tasks RCU. However, those early use cases that request multiple grace periods in quick succession are expected to do so from a single task, which makes the single lock almost irrelevant. If needed, multiple callback queues can be provided using any number of schemes. Perhaps most important, this variant of RCU does not affect the vanilla flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace readers can operate from idle, offline, and exception entry/exit in no way enables rcu_preempt and rcu_sched readers to do so. The memory ordering was outlined here: https://lore.kernel.org/lkml/20200319034030.GX3199@paulmck-ThinkPad-P72/ This effort benefited greatly from off-list discussions of BPF requirements with Alexei Starovoitov and Andrii Nakryiko. At least some of the on-list discussions are captured in the Link: tags below. In addition, KCSAN was quite helpful in finding some early bugs. Link: https://lore.kernel.org/lkml/20200219150744.428764577@infradead.org/ Link: https://lore.kernel.org/lkml/87mu8p797b.fsf@nanos.tec.linutronix.de/ Link: https://lore.kernel.org/lkml/20200225221305.605144982@linutronix.de/ Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com> Cc: Andrii Nakryiko <andriin@fb.com> [ paulmck: Apply feedback from Steve Rostedt and Joel Fernandes. ] [ paulmck: Decrement trc_n_readers_need_end upon IPI failure. ] [ paulmck: Fix locking issue reported by rcutorture. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Code movement to allow more Tasks RCU variantsPaul E. McKenney1-59/+63
This commit does nothing but move rcu_tasks_wait_gp() up to a new section for common code. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Further refactor RCU-tasks to allow adding more variantsPaul E. McKenney1-58/+108
This commit refactors RCU tasks to allow variants to be added. These variants will share the current Tasks-RCU tasklist scan and the holdout list processing. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Use unique names for RCU-Tasks kthreads and messagesPaul E. McKenney1-9/+16
This commit causes the flavors of RCU Tasks to use different names for their kthreads and in their console messages. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcutorture: Add torture tests for RCU Tasks RudePaul E. McKenney3-2/+32
This commit adds the definitions required to torture the rude flavor of RCU tasks. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Add an RCU-tasks rude variantPaul E. McKenney2-1/+108
This commit adds a "rude" variant of RCU-tasks that has as quiescent states schedule(), cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, anyway) cond_resched(). In other words, RCU-tasks rude readers are regions of code with preemption disabled, but excluding code early in the CPU-online sequence and late in the CPU-offline sequence. Updates make use of IPIs and force an IPI and a context switch on each online CPU. This variant is useful in some situations in tracing. Suggested-by: Steven Rostedt <rostedt@goodmis.org> [ paulmck: Apply EXPORT_SYMBOL_GPL() feedback from Qiujun Huang. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org> [ paulmck: Apply review feedback from Steve Rostedt. ]
2020-04-27rcu-tasks: Refactor RCU-tasks to allow variants to be addedPaul E. McKenney3-236/+269
This commit splits out generic processing from RCU-tasks-specific processing in order to allow additional flavors to be added. It also adds a def_bool TASKS_RCU_GENERIC to enable the common RCU-tasks infrastructure code. This is primarily, but not entirely, a code-movement commit. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcutorture: Add a test for synchronize_rcu_mult()Paul E. McKenney1-2/+7
This commit adds a crude test for synchronize_rcu_mult(). This is currently a smoke test rather than a high-quality stress test. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Create struct to hold state informationPaul E. McKenney1-27/+46
This commit creates an rcu_tasks struct to hold state information for RCU Tasks. This is a preparation commit for adding additional flavors of Tasks RCU, each of which would have its own rcu_tasks struct. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-04-27rcu-tasks: Move Tasks RCU to its own filePaul E. McKenney2-364/+372
This code-movement-only commit is in preparation for adding an additional flavor of Tasks RCU, which relies on workqueues to detect grace periods. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>