diff options
Diffstat (limited to 'kernel/context_tracking.c')
| -rw-r--r-- | kernel/context_tracking.c | 629 |
1 files changed, 569 insertions, 60 deletions
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 0296b4bda8f1..77978e372377 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -1,18 +1,20 @@ // SPDX-License-Identifier: GPL-2.0-only /* - * Context tracking: Probe on high level context boundaries such as kernel - * and userspace. This includes syscalls and exceptions entry/exit. + * Context tracking: Probe on high level context boundaries such as kernel, + * userspace, guest or idle. * * This is used by RCU to remove its dependency on the timer tick while a CPU - * runs in userspace. + * runs in idle, userspace or guest mode. * - * Started by Frederic Weisbecker: + * User/guest tracking started by Frederic Weisbecker: * - * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker <fweisbec@redhat.com> + * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker * * Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton, * Steven Rostedt, Peter Zijlstra for suggestions and improvements. * + * RCU extended quiescent state bits imported from kernel/rcu/tree.c + * where the relevant authorship may be found. */ #include <linux/context_tracking.h> @@ -21,6 +23,411 @@ #include <linux/hardirq.h> #include <linux/export.h> #include <linux/kprobes.h> +#include <trace/events/rcu.h> + + +DEFINE_PER_CPU(struct context_tracking, context_tracking) = { +#ifdef CONFIG_CONTEXT_TRACKING_IDLE + .dynticks_nesting = 1, + .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE, +#endif + .state = ATOMIC_INIT(RCU_DYNTICKS_IDX), +}; +EXPORT_SYMBOL_GPL(context_tracking); + +#ifdef CONFIG_CONTEXT_TRACKING_IDLE +#define TPS(x) tracepoint_string(x) + +/* Record the current task on dyntick-idle entry. */ +static __always_inline void rcu_dynticks_task_enter(void) +{ +#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) + WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); +#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ +} + +/* Record no current task on dyntick-idle exit. */ +static __always_inline void rcu_dynticks_task_exit(void) +{ +#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) + WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); +#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ +} + +/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */ +static __always_inline void rcu_dynticks_task_trace_enter(void) +{ +#ifdef CONFIG_TASKS_TRACE_RCU + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + current->trc_reader_special.b.need_mb = true; +#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ +} + +/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */ +static __always_inline void rcu_dynticks_task_trace_exit(void) +{ +#ifdef CONFIG_TASKS_TRACE_RCU + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + current->trc_reader_special.b.need_mb = false; +#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ +} + +/* + * Record entry into an extended quiescent state. This is only to be + * called when not already in an extended quiescent state, that is, + * RCU is watching prior to the call to this function and is no longer + * watching upon return. + */ +static noinstr void ct_kernel_exit_state(int offset) +{ + int seq; + + /* + * CPUs seeing atomic_add_return() must see prior RCU read-side + * critical sections, and we also must force ordering with the + * next idle sojourn. + */ + rcu_dynticks_task_trace_enter(); // Before ->dynticks update! + seq = ct_state_inc(offset); + // RCU is no longer watching. Better be in extended quiescent state! + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICKS_IDX)); +} + +/* + * Record exit from an extended quiescent state. This is only to be + * called from an extended quiescent state, that is, RCU is not watching + * prior to the call to this function and is watching upon return. + */ +static noinstr void ct_kernel_enter_state(int offset) +{ + int seq; + + /* + * CPUs seeing atomic_add_return() must see prior idle sojourns, + * and we also must force ordering with the next RCU read-side + * critical section. + */ + seq = ct_state_inc(offset); + // RCU is now watching. Better not be in an extended quiescent state! + rcu_dynticks_task_trace_exit(); // After ->dynticks update! + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICKS_IDX)); +} + +/* + * Enter an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. + * + * We crowbar the ->dynticks_nmi_nesting field to zero to allow for + * the possibility of usermode upcalls having messed up our count + * of interrupt nesting level during the prior busy period. + */ +static void noinstr ct_kernel_exit(bool user, int offset) +{ + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + + WARN_ON_ONCE(ct_dynticks_nmi_nesting() != DYNTICK_IRQ_NONIDLE); + WRITE_ONCE(ct->dynticks_nmi_nesting, 0); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + ct_dynticks_nesting() == 0); + if (ct_dynticks_nesting() != 1) { + // RCU will still be watching, so just do accounting and leave. + ct->dynticks_nesting--; + return; + } + + instrumentation_begin(); + lockdep_assert_irqs_disabled(); + trace_rcu_dyntick(TPS("Start"), ct_dynticks_nesting(), 0, ct_dynticks()); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); + rcu_preempt_deferred_qs(current); + + // instrumentation for the noinstr ct_kernel_exit_state() + instrument_atomic_write(&ct->state, sizeof(ct->state)); + + instrumentation_end(); + WRITE_ONCE(ct->dynticks_nesting, 0); /* Avoid irq-access tearing. */ + // RCU is watching here ... + ct_kernel_exit_state(offset); + // ... but is no longer watching here. + rcu_dynticks_task_enter(); +} + +/* + * Exit an RCU extended quiescent state, which can be either the + * idle loop or adaptive-tickless usermode execution. + * + * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to + * allow for the possibility of usermode upcalls messing up our count of + * interrupt nesting level during the busy period that is just now starting. + */ +static void noinstr ct_kernel_enter(bool user, int offset) +{ + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + long oldval; + + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); + oldval = ct_dynticks_nesting(); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); + if (oldval) { + // RCU was already watching, so just do accounting and leave. + ct->dynticks_nesting++; + return; + } + rcu_dynticks_task_exit(); + // RCU is not watching here ... + ct_kernel_enter_state(offset); + // ... but is watching here. + instrumentation_begin(); + + // instrumentation for the noinstr ct_kernel_enter_state() + instrument_atomic_write(&ct->state, sizeof(ct->state)); + + trace_rcu_dyntick(TPS("End"), ct_dynticks_nesting(), 1, ct_dynticks()); + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); + WRITE_ONCE(ct->dynticks_nesting, 1); + WARN_ON_ONCE(ct_dynticks_nmi_nesting()); + WRITE_ONCE(ct->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE); + instrumentation_end(); +} + +/** + * ct_nmi_exit - inform RCU of exit from NMI context + * + * If we are returning from the outermost NMI handler that interrupted an + * RCU-idle period, update ct->state and ct->dynticks_nmi_nesting + * to let the RCU grace-period handling know that the CPU is back to + * being RCU-idle. + * + * If you add or remove a call to ct_nmi_exit(), be sure to test + * with CONFIG_RCU_EQS_DEBUG=y. + */ +void noinstr ct_nmi_exit(void) +{ + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + + instrumentation_begin(); + /* + * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. + * (We are exiting an NMI handler, so RCU better be paying attention + * to us!) + */ + WARN_ON_ONCE(ct_dynticks_nmi_nesting() <= 0); + WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs()); + + /* + * If the nesting level is not 1, the CPU wasn't RCU-idle, so + * leave it in non-RCU-idle state. + */ + if (ct_dynticks_nmi_nesting() != 1) { + trace_rcu_dyntick(TPS("--="), ct_dynticks_nmi_nesting(), ct_dynticks_nmi_nesting() - 2, + ct_dynticks()); + WRITE_ONCE(ct->dynticks_nmi_nesting, /* No store tearing. */ + ct_dynticks_nmi_nesting() - 2); + instrumentation_end(); + return; + } + + /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ + trace_rcu_dyntick(TPS("Startirq"), ct_dynticks_nmi_nesting(), 0, ct_dynticks()); + WRITE_ONCE(ct->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ + + // instrumentation for the noinstr ct_kernel_exit_state() + instrument_atomic_write(&ct->state, sizeof(ct->state)); + instrumentation_end(); + + // RCU is watching here ... + ct_kernel_exit_state(RCU_DYNTICKS_IDX); + // ... but is no longer watching here. + + if (!in_nmi()) + rcu_dynticks_task_enter(); +} + +/** + * ct_nmi_enter - inform RCU of entry to NMI context + * + * If the CPU was idle from RCU's viewpoint, update ct->state and + * ct->dynticks_nmi_nesting to let the RCU grace-period handling know + * that the CPU is active. This implementation permits nested NMIs, as + * long as the nesting level does not overflow an int. (You will probably + * run out of stack space first.) + * + * If you add or remove a call to ct_nmi_enter(), be sure to test + * with CONFIG_RCU_EQS_DEBUG=y. + */ +void noinstr ct_nmi_enter(void) +{ + long incby = 2; + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + + /* Complain about underflow. */ + WARN_ON_ONCE(ct_dynticks_nmi_nesting() < 0); + + /* + * If idle from RCU viewpoint, atomically increment ->dynticks + * to mark non-idle and increment ->dynticks_nmi_nesting by one. + * Otherwise, increment ->dynticks_nmi_nesting by two. This means + * if ->dynticks_nmi_nesting is equal to one, we are guaranteed + * to be in the outermost NMI handler that interrupted an RCU-idle + * period (observation due to Andy Lutomirski). + */ + if (rcu_dynticks_curr_cpu_in_eqs()) { + + if (!in_nmi()) + rcu_dynticks_task_exit(); + + // RCU is not watching here ... + ct_kernel_enter_state(RCU_DYNTICKS_IDX); + // ... but is watching here. + + instrumentation_begin(); + // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs() + instrument_atomic_read(&ct->state, sizeof(ct->state)); + // instrumentation for the noinstr ct_kernel_enter_state() + instrument_atomic_write(&ct->state, sizeof(ct->state)); + + incby = 1; + } else if (!in_nmi()) { + instrumentation_begin(); + rcu_irq_enter_check_tick(); + } else { + instrumentation_begin(); + } + + trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), + ct_dynticks_nmi_nesting(), + ct_dynticks_nmi_nesting() + incby, ct_dynticks()); + instrumentation_end(); + WRITE_ONCE(ct->dynticks_nmi_nesting, /* Prevent store tearing. */ + ct_dynticks_nmi_nesting() + incby); + barrier(); +} + +/** + * ct_idle_enter - inform RCU that current CPU is entering idle + * + * Enter idle mode, in other words, -leave- the mode in which RCU + * read-side critical sections can occur. (Though RCU read-side + * critical sections can occur in irq handlers in idle, a possibility + * handled by irq_enter() and irq_exit().) + * + * If you add or remove a call to ct_idle_enter(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +void noinstr ct_idle_enter(void) +{ + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled()); + ct_kernel_exit(false, RCU_DYNTICKS_IDX + CONTEXT_IDLE); +} +EXPORT_SYMBOL_GPL(ct_idle_enter); + +/** + * ct_idle_exit - inform RCU that current CPU is leaving idle + * + * Exit idle mode, in other words, -enter- the mode in which RCU + * read-side critical sections can occur. + * + * If you add or remove a call to ct_idle_exit(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +void noinstr ct_idle_exit(void) +{ + unsigned long flags; + + raw_local_irq_save(flags); + ct_kernel_enter(false, RCU_DYNTICKS_IDX - CONTEXT_IDLE); + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(ct_idle_exit); + +/** + * ct_irq_enter - inform RCU that current CPU is entering irq away from idle + * + * Enter an interrupt handler, which might possibly result in exiting + * idle mode, in other words, entering the mode in which read-side critical + * sections can occur. The caller must have disabled interrupts. + * + * Note that the Linux kernel is fully capable of entering an interrupt + * handler that it never exits, for example when doing upcalls to user mode! + * This code assumes that the idle loop never does upcalls to user mode. + * If your architecture's idle loop does do upcalls to user mode (or does + * anything else that results in unbalanced calls to the irq_enter() and + * irq_exit() functions), RCU will give you what you deserve, good and hard. + * But very infrequently and irreproducibly. + * + * Use things like work queues to work around this limitation. + * + * You have been warned. + * + * If you add or remove a call to ct_irq_enter(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +noinstr void ct_irq_enter(void) +{ + lockdep_assert_irqs_disabled(); + ct_nmi_enter(); +} + +/** + * ct_irq_exit - inform RCU that current CPU is exiting irq towards idle + * + * Exit from an interrupt handler, which might possibly result in entering + * idle mode, in other words, leaving the mode in which read-side critical + * sections can occur. The caller must have disabled interrupts. + * + * This code assumes that the idle loop never does anything that might + * result in unbalanced calls to irq_enter() and irq_exit(). If your + * architecture's idle loop violates this assumption, RCU will give you what + * you deserve, good and hard. But very infrequently and irreproducibly. + * + * Use things like work queues to work around this limitation. + * + * You have been warned. + * + * If you add or remove a call to ct_irq_exit(), be sure to test with + * CONFIG_RCU_EQS_DEBUG=y. + */ +noinstr void ct_irq_exit(void) +{ + lockdep_assert_irqs_disabled(); + ct_nmi_exit(); +} + +/* + * Wrapper for ct_irq_enter() where interrupts are enabled. + * + * If you add or remove a call to ct_irq_enter_irqson(), be sure to test + * with CONFIG_RCU_EQS_DEBUG=y. + */ +void ct_irq_enter_irqson(void) +{ + unsigned long flags; + + local_irq_save(flags); + ct_irq_enter(); + local_irq_restore(flags); +} + +/* + * Wrapper for ct_irq_exit() where interrupts are enabled. + * + * If you add or remove a call to ct_irq_exit_irqson(), be sure to test + * with CONFIG_RCU_EQS_DEBUG=y. + */ +void ct_irq_exit_irqson(void) +{ + unsigned long flags; + + local_irq_save(flags); + ct_irq_exit(); + local_irq_restore(flags); +} +#else +static __always_inline void ct_kernel_exit(bool user, int offset) { } +static __always_inline void ct_kernel_enter(bool user, int offset) { } +#endif /* #ifdef CONFIG_CONTEXT_TRACKING_IDLE */ + +#ifdef CONFIG_CONTEXT_TRACKING_USER #define CREATE_TRACE_POINTS #include <trace/events/context_tracking.h> @@ -28,10 +435,7 @@ DEFINE_STATIC_KEY_FALSE(context_tracking_key); EXPORT_SYMBOL_GPL(context_tracking_key); -DEFINE_PER_CPU(struct context_tracking, context_tracking); -EXPORT_SYMBOL_GPL(context_tracking); - -static bool context_tracking_recursion_enter(void) +static noinstr bool context_tracking_recursion_enter(void) { int recursion; @@ -45,71 +449,117 @@ static bool context_tracking_recursion_enter(void) return false; } -static void context_tracking_recursion_exit(void) +static __always_inline void context_tracking_recursion_exit(void) { __this_cpu_dec(context_tracking.recursion); } /** - * context_tracking_enter - Inform the context tracking that the CPU is going - * enter user or guest space mode. + * __ct_user_enter - Inform the context tracking that the CPU is going + * to enter user or guest space mode. * * This function must be called right before we switch from the kernel * to user or guest space, when it's guaranteed the remaining kernel * instructions to execute won't use any RCU read side critical section * because this function sets RCU in extended quiescent state. */ -void __context_tracking_enter(enum ctx_state state) +void noinstr __ct_user_enter(enum ctx_state state) { + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + lockdep_assert_irqs_disabled(); + /* Kernel threads aren't supposed to go to userspace */ WARN_ON_ONCE(!current->mm); if (!context_tracking_recursion_enter()) return; - if ( __this_cpu_read(context_tracking.state) != state) { - if (__this_cpu_read(context_tracking.active)) { + if (__ct_state() != state) { + if (ct->active) { /* * At this stage, only low level arch entry code remains and * then we'll run in userspace. We can assume there won't be * any RCU read-side critical section until the next call to - * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency + * user_exit() or ct_irq_enter(). Let's remove RCU's dependency * on the tick. */ if (state == CONTEXT_USER) { + instrumentation_begin(); trace_user_enter(0); vtime_user_enter(current); + instrumentation_end(); + } + /* + * Other than generic entry implementation, we may be past the last + * rescheduling opportunity in the entry code. Trigger a self IPI + * that will fire and reschedule once we resume in user/guest mode. + */ + rcu_irq_work_resched(); + + /* + * Enter RCU idle mode right before resuming userspace. No use of RCU + * is permitted between this call and rcu_eqs_exit(). This way the + * CPU doesn't need to maintain the tick for RCU maintenance purposes + * when the CPU runs in userspace. + */ + ct_kernel_exit(true, RCU_DYNTICKS_IDX + state); + + /* + * Special case if we only track user <-> kernel transitions for tickless + * cputime accounting but we don't support RCU extended quiescent state. + * In this we case we don't care about any concurrency/ordering. + */ + if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) + atomic_set(&ct->state, state); + } else { + /* + * Even if context tracking is disabled on this CPU, because it's outside + * the full dynticks mask for example, we still have to keep track of the + * context transitions and states to prevent inconsistency on those of + * other CPUs. + * If a task triggers an exception in userspace, sleep on the exception + * handler and then migrate to another CPU, that new CPU must know where + * the exception returns by the time we call exception_exit(). + * This information can only be provided by the previous CPU when it called + * exception_enter(). + * OTOH we can spare the calls to vtime and RCU when context_tracking.active + * is false because we know that CPU is not tickless. + */ + if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) { + /* Tracking for vtime only, no concurrent RCU EQS accounting */ + atomic_set(&ct->state, state); + } else { + /* + * Tracking for vtime and RCU EQS. Make sure we don't race + * with NMIs. OTOH we don't care about ordering here since + * RCU only requires RCU_DYNTICKS_IDX increments to be fully + * ordered. + */ + atomic_add(state, &ct->state); } - rcu_user_enter(); } - /* - * Even if context tracking is disabled on this CPU, because it's outside - * the full dynticks mask for example, we still have to keep track of the - * context transitions and states to prevent inconsistency on those of - * other CPUs. - * If a task triggers an exception in userspace, sleep on the exception - * handler and then migrate to another CPU, that new CPU must know where - * the exception returns by the time we call exception_exit(). - * This information can only be provided by the previous CPU when it called - * exception_enter(). - * OTOH we can spare the calls to vtime and RCU when context_tracking.active - * is false because we know that CPU is not tickless. - */ - __this_cpu_write(context_tracking.state, state); } context_tracking_recursion_exit(); } -NOKPROBE_SYMBOL(__context_tracking_enter); -EXPORT_SYMBOL_GPL(__context_tracking_enter); +EXPORT_SYMBOL_GPL(__ct_user_enter); -void context_tracking_enter(enum ctx_state state) +/* + * OBSOLETE: + * This function should be noinstr but the below local_irq_restore() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call __context_tracking_enter() through user_enter_irqoff() + * or context_tracking_guest_enter(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ +void ct_user_enter(enum ctx_state state) { unsigned long flags; /* * Some contexts may involve an exception occuring in an irq, * leading to that nesting: - * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit() + * ct_irq_enter() rcu_eqs_exit(true) rcu_eqs_enter(true) ct_irq_exit() * This would mess up the dyntick_nesting count though. And rcu_irq_*() * helpers are enough to protect RCU uses inside the exception. So * just return immediately if we detect we are in an IRQ. @@ -118,21 +568,32 @@ void context_tracking_enter(enum ctx_state state) return; local_irq_save(flags); - __context_tracking_enter(state); + __ct_user_enter(state); local_irq_restore(flags); } -NOKPROBE_SYMBOL(context_tracking_enter); -EXPORT_SYMBOL_GPL(context_tracking_enter); +NOKPROBE_SYMBOL(ct_user_enter); +EXPORT_SYMBOL_GPL(ct_user_enter); -void context_tracking_user_enter(void) +/** + * user_enter_callable() - Unfortunate ASM callable version of user_enter() for + * archs that didn't manage to check the context tracking + * static key from low level code. + * + * This OBSOLETE function should be noinstr but it unsafely calls + * local_irq_restore(), involving illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call user_enter_irqoff(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ +void user_enter_callable(void) { user_enter(); } -NOKPROBE_SYMBOL(context_tracking_user_enter); +NOKPROBE_SYMBOL(user_enter_callable); /** - * context_tracking_exit - Inform the context tracking that the CPU is - * exiting user or guest mode and entering the kernel. + * __ct_user_exit - Inform the context tracking that the CPU is + * exiting user or guest mode and entering the kernel. * * This function must be called after we entered the kernel from user or * guest space before any use of RCU read side critical section. This @@ -142,31 +603,64 @@ NOKPROBE_SYMBOL(context_tracking_user_enter); * This call supports re-entrancy. This way it can be called from any exception * handler without needing to know if we came from userspace or not. */ -void __context_tracking_exit(enum ctx_state state) +void noinstr __ct_user_exit(enum ctx_state state) { + struct context_tracking *ct = this_cpu_ptr(&context_tracking); + if (!context_tracking_recursion_enter()) return; - if (__this_cpu_read(context_tracking.state) == state) { - if (__this_cpu_read(context_tracking.active)) { + if (__ct_state() == state) { + if (ct->active) { /* - * We are going to run code that may use RCU. Inform - * RCU core about that (ie: we may need the tick again). + * Exit RCU idle mode while entering the kernel because it can + * run a RCU read side critical section anytime. */ - rcu_user_exit(); + ct_kernel_enter(true, RCU_DYNTICKS_IDX - state); if (state == CONTEXT_USER) { + instrumentation_begin(); vtime_user_exit(current); trace_user_exit(0); + instrumentation_end(); + } + + /* + * Special case if we only track user <-> kernel transitions for tickless + * cputime accounting but we don't support RCU extended quiescent state. + * In this we case we don't care about any concurrency/ordering. + */ + if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) + atomic_set(&ct->state, CONTEXT_KERNEL); + + } else { + if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) { + /* Tracking for vtime only, no concurrent RCU EQS accounting */ + atomic_set(&ct->state, CONTEXT_KERNEL); + } else { + /* + * Tracking for vtime and RCU EQS. Make sure we don't race + * with NMIs. OTOH we don't care about ordering here since + * RCU only requires RCU_DYNTICKS_IDX increments to be fully + * ordered. + */ + atomic_sub(state, &ct->state); } } - __this_cpu_write(context_tracking.state, CONTEXT_KERNEL); } context_tracking_recursion_exit(); } -NOKPROBE_SYMBOL(__context_tracking_exit); -EXPORT_SYMBOL_GPL(__context_tracking_exit); +EXPORT_SYMBOL_GPL(__ct_user_exit); -void context_tracking_exit(enum ctx_state state) +/* + * OBSOLETE: + * This function should be noinstr but the below local_irq_save() is + * unsafe because it involves illegal RCU uses through tracing and lockdep. + * This is unlikely to be fixed as this function is obsolete. The preferred + * way is to call __context_tracking_exit() through user_exit_irqoff() + * or context_tracking_guest_exit(). It should be the arch entry code + * responsibility to call into context tracking with IRQs disabled. + */ +void ct_user_exit(enum ctx_state state) { unsigned long flags; @@ -174,19 +668,30 @@ void context_tracking_exit(enum ctx_state state) return; local_irq_save(flags); - __context_tracking_exit(state); + __ct_user_exit(state); local_irq_restore(flags); } -NOKPROBE_SYMBOL(context_tracking_exit); -EXPORT_SYMBOL_GPL(context_tracking_exit); +NOKPROBE_SYMBOL(ct_user_exit); +EXPORT_SYMBOL_GPL(ct_user_exit); -void context_tracking_user_exit(void) +/** + * user_exit_callable() - Unfortunate ASM callable version of user_exit() for + * archs that didn't manage to check the context tracking + * static key from low level code. + * + * This OBSOLETE function should be noinstr but it unsafely calls local_irq_save(), + * involving illegal RCU uses through tracing and lockdep. This is unlikely + * to be fixed as this function is obsolete. The preferred way is to call + * user_exit_irqoff(). It should be the arch entry code responsibility to + * call into context tracking with IRQs disabled. + */ +void user_exit_callable(void) { user_exit(); } -NOKPROBE_SYMBOL(context_tracking_user_exit); +NOKPROBE_SYMBOL(user_exit_callable); -void __init context_tracking_cpu_set(int cpu) +void __init ct_cpu_track_user(int cpu) { static __initdata bool initialized = false; @@ -198,22 +703,26 @@ void __init context_tracking_cpu_set(int cpu) if (initialized) return; +#ifdef CONFIG_HAVE_TIF_NOHZ /* * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork * This assumes that init is the only task at this early boot stage. */ set_tsk_thread_flag(&init_task, TIF_NOHZ); +#endif WARN_ON_ONCE(!tasklist_empty()); initialized = true; } -#ifdef CONFIG_CONTEXT_TRACKING_FORCE +#ifdef CONFIG_CONTEXT_TRACKING_USER_FORCE void __init context_tracking_init(void) { int cpu; for_each_possible_cpu(cpu) - context_tracking_cpu_set(cpu); + ct_cpu_track_user(cpu); } #endif + +#endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */ |