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![Peter Zijlstra](/assets/img/avatar_default.png)
Low level noinstr context-tracking code is calling out to instrumented code on KASAN: vmlinux.o: warning: objtool: __ct_user_enter+0x72: call to __kasan_check_write() leaves .noinstr.text section vmlinux.o: warning: objtool: __ct_user_exit+0x47: call to __kasan_check_write() leaves .noinstr.text section Use even lower level atomic methods to avoid the instrumentation. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20230112195542.458034262@infradead.org
728 lines
23 KiB
C
728 lines
23 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Context tracking: Probe on high level context boundaries such as kernel,
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* userspace, guest or idle.
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*
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* This is used by RCU to remove its dependency on the timer tick while a CPU
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* runs in idle, userspace or guest mode.
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*
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* User/guest tracking started by Frederic Weisbecker:
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*
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* Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker
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*
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* Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton,
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* Steven Rostedt, Peter Zijlstra for suggestions and improvements.
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*
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* RCU extended quiescent state bits imported from kernel/rcu/tree.c
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* where the relevant authorship may be found.
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*/
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#include <linux/context_tracking.h>
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#include <linux/rcupdate.h>
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#include <linux/sched.h>
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#include <linux/hardirq.h>
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#include <linux/export.h>
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#include <linux/kprobes.h>
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#include <trace/events/rcu.h>
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DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
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#ifdef CONFIG_CONTEXT_TRACKING_IDLE
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.dynticks_nesting = 1,
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.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
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#endif
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.state = ATOMIC_INIT(RCU_DYNTICKS_IDX),
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};
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EXPORT_SYMBOL_GPL(context_tracking);
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#ifdef CONFIG_CONTEXT_TRACKING_IDLE
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#define TPS(x) tracepoint_string(x)
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/* Record the current task on dyntick-idle entry. */
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static __always_inline void rcu_dynticks_task_enter(void)
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{
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#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
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WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
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#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
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}
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/* Record no current task on dyntick-idle exit. */
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static __always_inline void rcu_dynticks_task_exit(void)
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{
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#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
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WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
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#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
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}
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/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
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static __always_inline void rcu_dynticks_task_trace_enter(void)
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{
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#ifdef CONFIG_TASKS_TRACE_RCU
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if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
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current->trc_reader_special.b.need_mb = true;
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#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
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}
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/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
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static __always_inline void rcu_dynticks_task_trace_exit(void)
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{
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#ifdef CONFIG_TASKS_TRACE_RCU
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if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
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current->trc_reader_special.b.need_mb = false;
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#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
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}
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/*
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* Record entry into an extended quiescent state. This is only to be
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* called when not already in an extended quiescent state, that is,
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* RCU is watching prior to the call to this function and is no longer
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* watching upon return.
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*/
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static noinstr void ct_kernel_exit_state(int offset)
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{
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int seq;
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/*
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* CPUs seeing atomic_add_return() must see prior RCU read-side
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* critical sections, and we also must force ordering with the
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* next idle sojourn.
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*/
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rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
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seq = ct_state_inc(offset);
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// RCU is no longer watching. Better be in extended quiescent state!
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICKS_IDX));
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}
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/*
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* Record exit from an extended quiescent state. This is only to be
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* called from an extended quiescent state, that is, RCU is not watching
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* prior to the call to this function and is watching upon return.
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*/
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static noinstr void ct_kernel_enter_state(int offset)
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{
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int seq;
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/*
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* CPUs seeing atomic_add_return() must see prior idle sojourns,
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* and we also must force ordering with the next RCU read-side
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* critical section.
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*/
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seq = ct_state_inc(offset);
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// RCU is now watching. Better not be in an extended quiescent state!
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rcu_dynticks_task_trace_exit(); // After ->dynticks update!
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICKS_IDX));
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}
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/*
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* Enter an RCU extended quiescent state, which can be either the
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* idle loop or adaptive-tickless usermode execution.
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*
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* We crowbar the ->dynticks_nmi_nesting field to zero to allow for
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* the possibility of usermode upcalls having messed up our count
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* of interrupt nesting level during the prior busy period.
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*/
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static void noinstr ct_kernel_exit(bool user, int offset)
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{
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struct context_tracking *ct = this_cpu_ptr(&context_tracking);
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WARN_ON_ONCE(ct_dynticks_nmi_nesting() != DYNTICK_IRQ_NONIDLE);
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WRITE_ONCE(ct->dynticks_nmi_nesting, 0);
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
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ct_dynticks_nesting() == 0);
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if (ct_dynticks_nesting() != 1) {
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// RCU will still be watching, so just do accounting and leave.
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ct->dynticks_nesting--;
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return;
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}
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instrumentation_begin();
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lockdep_assert_irqs_disabled();
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trace_rcu_dyntick(TPS("Start"), ct_dynticks_nesting(), 0, ct_dynticks());
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
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rcu_preempt_deferred_qs(current);
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// instrumentation for the noinstr ct_kernel_exit_state()
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instrument_atomic_write(&ct->state, sizeof(ct->state));
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instrumentation_end();
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WRITE_ONCE(ct->dynticks_nesting, 0); /* Avoid irq-access tearing. */
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// RCU is watching here ...
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ct_kernel_exit_state(offset);
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// ... but is no longer watching here.
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rcu_dynticks_task_enter();
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}
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/*
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* Exit an RCU extended quiescent state, which can be either the
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* idle loop or adaptive-tickless usermode execution.
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*
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* We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
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* allow for the possibility of usermode upcalls messing up our count of
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* interrupt nesting level during the busy period that is just now starting.
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*/
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static void noinstr ct_kernel_enter(bool user, int offset)
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{
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struct context_tracking *ct = this_cpu_ptr(&context_tracking);
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long oldval;
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
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oldval = ct_dynticks_nesting();
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
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if (oldval) {
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// RCU was already watching, so just do accounting and leave.
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ct->dynticks_nesting++;
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return;
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}
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rcu_dynticks_task_exit();
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// RCU is not watching here ...
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ct_kernel_enter_state(offset);
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// ... but is watching here.
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instrumentation_begin();
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// instrumentation for the noinstr ct_kernel_enter_state()
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instrument_atomic_write(&ct->state, sizeof(ct->state));
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trace_rcu_dyntick(TPS("End"), ct_dynticks_nesting(), 1, ct_dynticks());
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
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WRITE_ONCE(ct->dynticks_nesting, 1);
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WARN_ON_ONCE(ct_dynticks_nmi_nesting());
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WRITE_ONCE(ct->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
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instrumentation_end();
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}
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/**
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* ct_nmi_exit - inform RCU of exit from NMI context
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*
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* If we are returning from the outermost NMI handler that interrupted an
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* RCU-idle period, update ct->state and ct->dynticks_nmi_nesting
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* to let the RCU grace-period handling know that the CPU is back to
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* being RCU-idle.
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*
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* If you add or remove a call to ct_nmi_exit(), be sure to test
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* with CONFIG_RCU_EQS_DEBUG=y.
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*/
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void noinstr ct_nmi_exit(void)
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{
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struct context_tracking *ct = this_cpu_ptr(&context_tracking);
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instrumentation_begin();
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/*
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* Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
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* (We are exiting an NMI handler, so RCU better be paying attention
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* to us!)
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*/
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WARN_ON_ONCE(ct_dynticks_nmi_nesting() <= 0);
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WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
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/*
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* If the nesting level is not 1, the CPU wasn't RCU-idle, so
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* leave it in non-RCU-idle state.
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*/
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if (ct_dynticks_nmi_nesting() != 1) {
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trace_rcu_dyntick(TPS("--="), ct_dynticks_nmi_nesting(), ct_dynticks_nmi_nesting() - 2,
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ct_dynticks());
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WRITE_ONCE(ct->dynticks_nmi_nesting, /* No store tearing. */
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ct_dynticks_nmi_nesting() - 2);
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instrumentation_end();
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return;
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}
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/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
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trace_rcu_dyntick(TPS("Startirq"), ct_dynticks_nmi_nesting(), 0, ct_dynticks());
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WRITE_ONCE(ct->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
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// instrumentation for the noinstr ct_kernel_exit_state()
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instrument_atomic_write(&ct->state, sizeof(ct->state));
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instrumentation_end();
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// RCU is watching here ...
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ct_kernel_exit_state(RCU_DYNTICKS_IDX);
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// ... but is no longer watching here.
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if (!in_nmi())
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rcu_dynticks_task_enter();
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}
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/**
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* ct_nmi_enter - inform RCU of entry to NMI context
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*
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* If the CPU was idle from RCU's viewpoint, update ct->state and
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* ct->dynticks_nmi_nesting to let the RCU grace-period handling know
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* that the CPU is active. This implementation permits nested NMIs, as
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* long as the nesting level does not overflow an int. (You will probably
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* run out of stack space first.)
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*
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* If you add or remove a call to ct_nmi_enter(), be sure to test
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* with CONFIG_RCU_EQS_DEBUG=y.
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*/
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void noinstr ct_nmi_enter(void)
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{
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long incby = 2;
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struct context_tracking *ct = this_cpu_ptr(&context_tracking);
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/* Complain about underflow. */
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WARN_ON_ONCE(ct_dynticks_nmi_nesting() < 0);
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/*
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* If idle from RCU viewpoint, atomically increment ->dynticks
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* to mark non-idle and increment ->dynticks_nmi_nesting by one.
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* Otherwise, increment ->dynticks_nmi_nesting by two. This means
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* if ->dynticks_nmi_nesting is equal to one, we are guaranteed
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* to be in the outermost NMI handler that interrupted an RCU-idle
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* period (observation due to Andy Lutomirski).
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*/
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if (rcu_dynticks_curr_cpu_in_eqs()) {
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if (!in_nmi())
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rcu_dynticks_task_exit();
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// RCU is not watching here ...
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ct_kernel_enter_state(RCU_DYNTICKS_IDX);
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// ... but is watching here.
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instrumentation_begin();
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// instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
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instrument_atomic_read(&ct->state, sizeof(ct->state));
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// instrumentation for the noinstr ct_kernel_enter_state()
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instrument_atomic_write(&ct->state, sizeof(ct->state));
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incby = 1;
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} else if (!in_nmi()) {
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instrumentation_begin();
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rcu_irq_enter_check_tick();
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} else {
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instrumentation_begin();
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}
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trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
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ct_dynticks_nmi_nesting(),
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ct_dynticks_nmi_nesting() + incby, ct_dynticks());
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instrumentation_end();
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WRITE_ONCE(ct->dynticks_nmi_nesting, /* Prevent store tearing. */
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ct_dynticks_nmi_nesting() + incby);
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barrier();
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}
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/**
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* ct_idle_enter - inform RCU that current CPU is entering idle
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*
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* Enter idle mode, in other words, -leave- the mode in which RCU
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* read-side critical sections can occur. (Though RCU read-side
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* critical sections can occur in irq handlers in idle, a possibility
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* handled by irq_enter() and irq_exit().)
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*
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* If you add or remove a call to ct_idle_enter(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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void noinstr ct_idle_enter(void)
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{
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
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ct_kernel_exit(false, RCU_DYNTICKS_IDX + CONTEXT_IDLE);
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}
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EXPORT_SYMBOL_GPL(ct_idle_enter);
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/**
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* ct_idle_exit - inform RCU that current CPU is leaving idle
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*
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* Exit idle mode, in other words, -enter- the mode in which RCU
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* read-side critical sections can occur.
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*
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* If you add or remove a call to ct_idle_exit(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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void noinstr ct_idle_exit(void)
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{
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unsigned long flags;
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raw_local_irq_save(flags);
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ct_kernel_enter(false, RCU_DYNTICKS_IDX - CONTEXT_IDLE);
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raw_local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(ct_idle_exit);
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/**
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* ct_irq_enter - inform RCU that current CPU is entering irq away from idle
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*
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* Enter an interrupt handler, which might possibly result in exiting
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* idle mode, in other words, entering the mode in which read-side critical
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* sections can occur. The caller must have disabled interrupts.
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*
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* Note that the Linux kernel is fully capable of entering an interrupt
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* handler that it never exits, for example when doing upcalls to user mode!
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* This code assumes that the idle loop never does upcalls to user mode.
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* If your architecture's idle loop does do upcalls to user mode (or does
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* anything else that results in unbalanced calls to the irq_enter() and
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* irq_exit() functions), RCU will give you what you deserve, good and hard.
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* But very infrequently and irreproducibly.
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*
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* Use things like work queues to work around this limitation.
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*
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* You have been warned.
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*
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* If you add or remove a call to ct_irq_enter(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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noinstr void ct_irq_enter(void)
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{
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lockdep_assert_irqs_disabled();
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ct_nmi_enter();
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}
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/**
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* ct_irq_exit - inform RCU that current CPU is exiting irq towards idle
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*
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* Exit from an interrupt handler, which might possibly result in entering
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* idle mode, in other words, leaving the mode in which read-side critical
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* sections can occur. The caller must have disabled interrupts.
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*
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* This code assumes that the idle loop never does anything that might
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* result in unbalanced calls to irq_enter() and irq_exit(). If your
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* architecture's idle loop violates this assumption, RCU will give you what
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* you deserve, good and hard. But very infrequently and irreproducibly.
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*
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* Use things like work queues to work around this limitation.
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*
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* You have been warned.
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*
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* If you add or remove a call to ct_irq_exit(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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noinstr void ct_irq_exit(void)
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{
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lockdep_assert_irqs_disabled();
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ct_nmi_exit();
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}
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/*
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* Wrapper for ct_irq_enter() where interrupts are enabled.
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*
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* If you add or remove a call to ct_irq_enter_irqson(), be sure to test
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* with CONFIG_RCU_EQS_DEBUG=y.
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*/
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void ct_irq_enter_irqson(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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ct_irq_enter();
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local_irq_restore(flags);
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}
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/*
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* Wrapper for ct_irq_exit() where interrupts are enabled.
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*
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* If you add or remove a call to ct_irq_exit_irqson(), be sure to test
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* with CONFIG_RCU_EQS_DEBUG=y.
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*/
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void ct_irq_exit_irqson(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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ct_irq_exit();
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local_irq_restore(flags);
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}
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#else
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static __always_inline void ct_kernel_exit(bool user, int offset) { }
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static __always_inline void ct_kernel_enter(bool user, int offset) { }
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#endif /* #ifdef CONFIG_CONTEXT_TRACKING_IDLE */
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#ifdef CONFIG_CONTEXT_TRACKING_USER
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#define CREATE_TRACE_POINTS
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#include <trace/events/context_tracking.h>
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DEFINE_STATIC_KEY_FALSE(context_tracking_key);
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EXPORT_SYMBOL_GPL(context_tracking_key);
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static noinstr bool context_tracking_recursion_enter(void)
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{
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int recursion;
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recursion = __this_cpu_inc_return(context_tracking.recursion);
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if (recursion == 1)
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return true;
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|
|
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))
|
|
arch_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 */
|
|
arch_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.
|
|
*/
|
|
arch_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))
|
|
arch_atomic_set(&ct->state, CONTEXT_KERNEL);
|
|
|
|
} else {
|
|
if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
|
|
/* Tracking for vtime only, no concurrent RCU EQS accounting */
|
|
arch_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.
|
|
*/
|
|
arch_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 */
|