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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
commitace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch)
treeb2d64bc10158fdd5497876388cd68142ca374ed3 /kernel/context_tracking.c
parentInitial commit. (diff)
downloadlinux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz
linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'kernel/context_tracking.c')
-rw-r--r--kernel/context_tracking.c728
1 files changed, 728 insertions, 0 deletions
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
new file mode 100644
index 0000000000..6ef0b35fc2
--- /dev/null
+++ b/kernel/context_tracking.c
@@ -0,0 +1,728 @@
+// 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
+ .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>
+
+DEFINE_STATIC_KEY_FALSE(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.
+ *
+ * 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 == 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))
+ raw_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 */
+ raw_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.
+ */
+ raw_atomic_add(state, &ct->state);
+ }
+ }
+ }
+ context_tracking_recursion_exit();
+}
+EXPORT_SYMBOL_GPL(__ct_user_enter);
+
+/*
+ * 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:
+ * 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.
+ */
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __ct_user_enter(state);
+ local_irq_restore(flags);
+}
+NOKPROBE_SYMBOL(ct_user_enter);
+EXPORT_SYMBOL_GPL(ct_user_enter);
+
+/**
+ * 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(user_enter_callable);
+
+/**
+ * __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
+ * potentially include any high level kernel code like syscalls, exceptions,
+ * signal handling, etc...
+ *
+ * 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 noinstr __ct_user_exit(enum ctx_state state)
+{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
+
+ if (!context_tracking_recursion_enter())
+ return;
+
+ if (__ct_state() == state) {
+ if (ct->active) {
+ /*
+ * Exit RCU idle mode while entering the kernel because it can
+ * run a RCU read side critical section anytime.
+ */
+ 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))
+ raw_atomic_set(&ct->state, CONTEXT_KERNEL);
+
+ } else {
+ if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
+ /* Tracking for vtime only, no concurrent RCU EQS accounting */
+ raw_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.
+ */
+ raw_atomic_sub(state, &ct->state);
+ }
+ }
+ }
+ context_tracking_recursion_exit();
+}
+EXPORT_SYMBOL_GPL(__ct_user_exit);
+
+/*
+ * 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;
+
+ if (in_interrupt())
+ return;
+
+ local_irq_save(flags);
+ __ct_user_exit(state);
+ local_irq_restore(flags);
+}
+NOKPROBE_SYMBOL(ct_user_exit);
+EXPORT_SYMBOL_GPL(ct_user_exit);
+
+/**
+ * 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(user_exit_callable);
+
+void __init ct_cpu_track_user(int cpu)
+{
+ static __initdata bool initialized = false;
+
+ if (!per_cpu(context_tracking.active, cpu)) {
+ per_cpu(context_tracking.active, cpu) = true;
+ static_branch_inc(&context_tracking_key);
+ }
+
+ 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_USER_FORCE
+void __init context_tracking_init(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ ct_cpu_track_user(cpu);
+}
+#endif
+
+#endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */