// SPDX-License-Identifier: GPL-2.0-only/* * 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 idle, userspace or guest mode. * * User/guest tracking started by Frederic Weisbecker: * * 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>#include <linux/rcupdate.h>#include <linux/sched.h>#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	.nesting = 1,	.nmi_nesting = CT_NESTING_IRQ_NONIDLE,#endif	.state = ATOMIC_INIT(CT_RCU_WATCHING),};EXPORT_SYMBOL_GPL(context_tracking); #ifdef CONFIG_CONTEXT_TRACKING_IDLE#define TPS(x)  tracepoint_string(x) /* Record the current task on exiting RCU-tasks (dyntick-idle entry). */static __always_inline void rcu_task_exit(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 entering RCU-tasks (dyntick-idle exit). */static __always_inline void rcu_task_enter(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 kernel exit. */static __always_inline void rcu_task_trace_heavyweight_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 kernel entry. */static __always_inline void rcu_task_trace_heavyweight_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){	/*	 * 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_task_trace_heavyweight_enter();  // Before CT state update!	// RCU is still watching.  Better not be in extended quiescent state!	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !rcu_is_watching_curr_cpu());	(void)ct_state_inc(offset);	// RCU is no longer watching.} /* * 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_task_trace_heavyweight_exit();  // After CT state update!	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & CT_RCU_WATCHING));} /* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. * * We crowbar the ->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_nmi_nesting() != CT_NESTING_IRQ_NONIDLE);	WRITE_ONCE(ct->nmi_nesting, 0);	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&		     ct_nesting() == 0);	if (ct_nesting() != 1) {		// RCU will still be watching, so just do accounting and leave.		ct->nesting--;		return;	} 	instrumentation_begin();	lockdep_assert_irqs_disabled();	trace_rcu_watching(TPS("End"), ct_nesting(), 0, ct_rcu_watching());	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->nesting, 0); /* Avoid irq-access tearing. */	// RCU is watching here ...	ct_kernel_exit_state(offset);	// ... but is no longer watching here.	rcu_task_exit();} /* * Exit an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. * * We crowbar the ->nmi_nesting field to CT_NESTING_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_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->nesting++;		return;	}	rcu_task_enter();	// 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_watching(TPS("Start"), ct_nesting(), 1, ct_rcu_watching());	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));	WRITE_ONCE(ct->nesting, 1);	WARN_ON_ONCE(ct_nmi_nesting());	WRITE_ONCE(ct->nmi_nesting, CT_NESTING_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->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 ->nmi_nesting underflow and bad CT state.	 * (We are exiting an NMI handler, so RCU better be paying attention	 * to us!)	 */	WARN_ON_ONCE(ct_nmi_nesting() <= 0);	WARN_ON_ONCE(!rcu_is_watching_curr_cpu()); 	/*	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so	 * leave it in non-RCU-idle state.	 */	if (ct_nmi_nesting() != 1) {		trace_rcu_watching(TPS("--="), ct_nmi_nesting(), ct_nmi_nesting() - 2,				  ct_rcu_watching());		WRITE_ONCE(ct->nmi_nesting, /* No store tearing. */			   ct_nmi_nesting() - 2);		instrumentation_end();		return;	} 	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */	trace_rcu_watching(TPS("Endirq"), ct_nmi_nesting(), 0, ct_rcu_watching());	WRITE_ONCE(ct->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(CT_RCU_WATCHING);	// ... but is no longer watching here. 	if (!in_nmi())		rcu_task_exit();} /** * ct_nmi_enter - inform RCU of entry to NMI context * * If the CPU was idle from RCU's viewpoint, update ct->state and * ct->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_nmi_nesting() < 0); 	/*	 * If idle from RCU viewpoint, atomically increment CT state	 * to mark non-idle and increment ->nmi_nesting by one.	 * Otherwise, increment ->nmi_nesting by two.  This means	 * if ->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_is_watching_curr_cpu()) { 		if (!in_nmi())			rcu_task_enter(); 		// RCU is not watching here ...		ct_kernel_enter_state(CT_RCU_WATCHING);		// ... but is watching here. 		instrumentation_begin();		// instrumentation for the noinstr rcu_is_watching_curr_cpu()		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_watching(incby == 1 ? TPS("Startirq") : TPS("++="),			  ct_nmi_nesting(),			  ct_nmi_nesting() + incby, ct_rcu_watching());	instrumentation_end();	WRITE_ONCE(ct->nmi_nesting, /* Prevent store tearing. */		   ct_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, CT_RCU_WATCHING + CT_STATE_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, CT_RCU_WATCHING - CT_STATE_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);}#elsestatic __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> DEFINE_STATIC_KEY_FALSE_RO(context_tracking_key);EXPORT_SYMBOL_GPL(context_tracking_key); static noinstr bool context_tracking_recursion_enter(void){	int recursion; 	recursion = __this_cpu_inc_return(context_tracking.recursion);	if (recursion == 1)		return true; 	WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion);	__this_cpu_dec(context_tracking.recursion); 	return false;} static __always_inline void context_tracking_recursion_exit(void){	__this_cpu_dec(context_tracking.recursion);} /** * __ct_user_enter - Inform the context tracking that the CPU is going *		     to enter user or guest space mode. * * @state: userspace context-tracking state to enter. * * 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 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 (__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 ct_irq_enter(). Let's remove RCU's dependency			 * on the tick.			 */			if (state == CT_STATE_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(); 			/*

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