forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
728 lines
23 KiB
728 lines
23 KiB
// 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)) |
|
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); |
|
} |
|
} |
|
} |
|
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)) |
|
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); |
|
} |
|
} |
|
} |
|
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 */
|
|
|