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context_tracking: Convert state to atomic_t

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Context tracking's state and dynticks counter are going to be merged
in a single field so that both updates can happen atomically and at the
same time. Prepare for that with converting the state into an atomic_t.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
This commit is contained in:
Frederic Weisbecker 2022-06-08 16:40:35 +02:00 committed by Paul E. McKenney
parent c33ef43a35
commit 171476775d
5 changed files with 159 additions and 92 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
include/linux/context_tracking.h
View File

@ -56,7 +56,7 @@ static inline enum ctx_state exception_enter(void)
!context_tracking_enabled())
return 0;
prev_ctx = this_cpu_read(context_tracking.state);
prev_ctx = __ct_state();
if (prev_ctx != CONTEXT_KERNEL)
ct_user_exit(prev_ctx);
@ -86,33 +86,21 @@ static __always_inline void context_tracking_guest_exit(void)
__ct_user_exit(CONTEXT_GUEST);
}
/**
* ct_state() - return the current context tracking state if known
*
* Returns the current cpu's context tracking state if context tracking
* is enabled. If context tracking is disabled, returns
* CONTEXT_DISABLED. This should be used primarily for debugging.
*/
static __always_inline enum ctx_state ct_state(void)
{
return context_tracking_enabled() ?
this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
}
#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
#else
static inline void user_enter(void) { }
static inline void user_exit(void) { }
static inline void user_enter_irqoff(void) { }
static inline void user_exit_irqoff(void) { }
static inline enum ctx_state exception_enter(void) { return 0; }
static inline int exception_enter(void) { return 0; }
static inline void exception_exit(enum ctx_state prev_ctx) { }
static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
static inline int ct_state(void) { return -1; }
static __always_inline bool context_tracking_guest_enter(void) { return false; }
static inline void context_tracking_guest_exit(void) { }
#define CT_WARN_ON(cond) do { } while (0)
#endif /* !CONFIG_CONTEXT_TRACKING_USER */
#define CT_WARN_ON(cond) WARN_ON(context_tracking_enabled() && (cond))
#ifdef CONFIG_CONTEXT_TRACKING_USER_FORCE
extern void context_tracking_init(void);
#else
@ -130,16 +118,16 @@ extern void ct_idle_exit(void);
*/
static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
{
return !(arch_atomic_read(this_cpu_ptr(&context_tracking.dynticks)) & 0x1);
return !(arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & RCU_DYNTICKS_IDX);
}
/*
* Increment the current CPU's context_tracking structure's ->dynticks field
* Increment the current CPU's context_tracking structure's ->state field
* with ordering. Return the new value.
*/
static __always_inline unsigned long rcu_dynticks_inc(int incby)
static __always_inline unsigned long ct_state_inc(int incby)
{
return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.dynticks));
return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.state));
}
#else

53
include/linux/context_tracking_state.h
View File

@ -6,15 +6,23 @@
#include <linux/static_key.h>
#include <linux/context_tracking_irq.h>
/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
#define DYNTICK_IRQ_NONIDLE ((LONG_MAX / 2) + 1)
enum ctx_state {
CONTEXT_DISABLED = -1, /* returned by ct_state() if unknown */
CONTEXT_KERNEL = 0,
CONTEXT_USER,
CONTEXT_GUEST,
CONTEXT_IDLE = 1,
CONTEXT_USER = 2,
CONTEXT_GUEST = 3,
CONTEXT_MAX = 4,
};
/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
#define DYNTICK_IRQ_NONIDLE ((LONG_MAX / 2) + 1)
/* Even value for idle, else odd. */
#define RCU_DYNTICKS_IDX CONTEXT_MAX
#define CT_STATE_MASK (CONTEXT_MAX - 1)
#define CT_DYNTICKS_MASK (~CT_STATE_MASK)
struct context_tracking {
#ifdef CONFIG_CONTEXT_TRACKING_USER
@ -26,10 +34,11 @@ struct context_tracking {
*/
bool active;
int recursion;
enum ctx_state state;
#endif
#ifdef CONFIG_CONTEXT_TRACKING
atomic_t state;
#endif
#ifdef CONFIG_CONTEXT_TRACKING_IDLE
atomic_t dynticks; /* Even value for idle, else odd. */
long dynticks_nesting; /* Track process nesting level. */
long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
#endif
@ -37,26 +46,31 @@ struct context_tracking {
#ifdef CONFIG_CONTEXT_TRACKING
DECLARE_PER_CPU(struct context_tracking, context_tracking);
static __always_inline int __ct_state(void)
{
return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
}
#endif
#ifdef CONFIG_CONTEXT_TRACKING_IDLE
static __always_inline int ct_dynticks(void)
{
return atomic_read(this_cpu_ptr(&context_tracking.dynticks));
return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_DYNTICKS_MASK;
}
static __always_inline int ct_dynticks_cpu(int cpu)
{
struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
return atomic_read(&ct->dynticks);
return atomic_read(&ct->state) & CT_DYNTICKS_MASK;
}
static __always_inline int ct_dynticks_cpu_acquire(int cpu)
{
struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
return atomic_read_acquire(&ct->dynticks);
return atomic_read_acquire(&ct->state) & CT_DYNTICKS_MASK;
}
static __always_inline long ct_dynticks_nesting(void)
@ -102,6 +116,27 @@ static inline bool context_tracking_enabled_this_cpu(void)
return context_tracking_enabled() && __this_cpu_read(context_tracking.active);
}
/**
* ct_state() - return the current context tracking state if known
*
* Returns the current cpu's context tracking state if context tracking
* is enabled. If context tracking is disabled, returns
* CONTEXT_DISABLED. This should be used primarily for debugging.
*/
static __always_inline int ct_state(void)
{
int ret;
if (!context_tracking_enabled())
return CONTEXT_DISABLED;
preempt_disable();
ret = __ct_state();
preempt_enable();
return ret;
}
#else
static __always_inline bool context_tracking_enabled(void) { return false; }
static __always_inline bool context_tracking_enabled_cpu(int cpu) { return false; }

119
kernel/context_tracking.c
View File

@ -28,8 +28,8 @@ DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
#ifdef CONFIG_CONTEXT_TRACKING_IDLE
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
.dynticks = ATOMIC_INIT(1),
#endif
.state = ATOMIC_INIT(RCU_DYNTICKS_IDX),
};
EXPORT_SYMBOL_GPL(context_tracking);
@ -76,7 +76,7 @@ static __always_inline void rcu_dynticks_task_trace_exit(void)
* RCU is watching prior to the call to this function and is no longer
* watching upon return.
*/
static noinstr void rcu_dynticks_eqs_enter(void)
static noinstr void ct_kernel_exit_state(int offset)
{
int seq;
@ -86,9 +86,9 @@ static noinstr void rcu_dynticks_eqs_enter(void)
* next idle sojourn.
*/
rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
seq = rcu_dynticks_inc(1);
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 & 0x1));
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICKS_IDX));
}
/*
@ -96,7 +96,7 @@ static noinstr void rcu_dynticks_eqs_enter(void)
* 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 rcu_dynticks_eqs_exit(void)
static noinstr void ct_kernel_enter_state(int offset)
{
int seq;
@ -105,10 +105,10 @@ static noinstr void rcu_dynticks_eqs_exit(void)
* and we also must force ordering with the next RCU read-side
* critical section.
*/
seq = rcu_dynticks_inc(1);
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 & 0x1));
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICKS_IDX));
}
/*
@ -119,7 +119,7 @@ static noinstr void rcu_dynticks_eqs_exit(void)
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*/
static void noinstr rcu_eqs_enter(bool user)
static void noinstr ct_kernel_exit(bool user, int offset)
{
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
@ -139,13 +139,13 @@ static void noinstr rcu_eqs_enter(bool user)
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
rcu_preempt_deferred_qs(current);
// instrumentation for the noinstr rcu_dynticks_eqs_enter()
instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
// 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 ...
rcu_dynticks_eqs_enter();
ct_kernel_exit_state(offset);
// ... but is no longer watching here.
rcu_dynticks_task_enter();
}
@ -158,7 +158,7 @@ static void noinstr rcu_eqs_enter(bool user)
* 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 rcu_eqs_exit(bool user)
static void noinstr ct_kernel_enter(bool user, int offset)
{
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
long oldval;
@ -173,12 +173,12 @@ static void noinstr rcu_eqs_exit(bool user)
}
rcu_dynticks_task_exit();
// RCU is not watching here ...
rcu_dynticks_eqs_exit();
ct_kernel_enter_state(offset);
// ... but is watching here.
instrumentation_begin();
// instrumentation for the noinstr rcu_dynticks_eqs_exit()
instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
// 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));
@ -192,7 +192,7 @@ static void noinstr rcu_eqs_exit(bool user)
* 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->dynticks and ct->dynticks_nmi_nesting
* 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.
*
@ -229,12 +229,12 @@ void noinstr ct_nmi_exit(void)
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 rcu_dynticks_eqs_enter()
instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
// instrumentation for the noinstr ct_kernel_exit_state()
instrument_atomic_write(&ct->state, sizeof(ct->state));
instrumentation_end();
// RCU is watching here ...
rcu_dynticks_eqs_enter();
ct_kernel_exit_state(RCU_DYNTICKS_IDX);
// ... but is no longer watching here.
if (!in_nmi())
@ -244,7 +244,7 @@ void noinstr ct_nmi_exit(void)
/**
* ct_nmi_enter - inform RCU of entry to NMI context
*
* If the CPU was idle from RCU's viewpoint, update ct->dynticks and
* 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
@ -275,14 +275,14 @@ void noinstr ct_nmi_enter(void)
rcu_dynticks_task_exit();
// RCU is not watching here ...
rcu_dynticks_eqs_exit();
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->dynticks, sizeof(ct->dynticks));
// instrumentation for the noinstr rcu_dynticks_eqs_exit()
instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
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()) {
@ -315,7 +315,7 @@ void noinstr ct_nmi_enter(void)
void noinstr ct_idle_enter(void)
{
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
rcu_eqs_enter(false);
ct_kernel_exit(false, RCU_DYNTICKS_IDX + CONTEXT_IDLE);
}
EXPORT_SYMBOL_GPL(ct_idle_enter);
@ -333,7 +333,7 @@ void noinstr ct_idle_exit(void)
unsigned long flags;
raw_local_irq_save(flags);
rcu_eqs_exit(false);
ct_kernel_enter(false, RCU_DYNTICKS_IDX - CONTEXT_IDLE);
raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(ct_idle_exit);
@ -421,8 +421,8 @@ void ct_irq_exit_irqson(void)
local_irq_restore(flags);
}
#else
static __always_inline void rcu_eqs_enter(bool user) { }
static __always_inline void rcu_eqs_exit(bool user) { }
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
@ -463,6 +463,7 @@ static __always_inline void context_tracking_recursion_exit(void)
*/
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 */
@ -471,8 +472,8 @@ void noinstr __ct_user_enter(enum ctx_state state)
if (!context_tracking_recursion_enter())
return;
if ( __this_cpu_read(context_tracking.state) != state) {
if (__this_cpu_read(context_tracking.active)) {
if (__ct_state() != state) {
if (ct->active) {
/*
* At this stage, only low level arch entry code remains and
* then we'll run in userspace. We can assume there won't be
@ -492,14 +493,23 @@ void noinstr __ct_user_enter(enum ctx_state state)
* 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.
*/
rcu_eqs_enter(true);
}
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
@ -513,7 +523,19 @@ void noinstr __ct_user_enter(enum ctx_state state)
* OTOH we can spare the calls to vtime and RCU when context_tracking.active
* is false because we know that CPU is not tickless.
*/
__this_cpu_write(context_tracking.state, state);
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();
}
@ -581,24 +603,47 @@ NOKPROBE_SYMBOL(user_enter_callable);
*/
void noinstr __ct_user_exit(enum ctx_state state)
{
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
if (!context_tracking_recursion_enter())
return;
if (__this_cpu_read(context_tracking.state) == state) {
if (__this_cpu_read(context_tracking.active)) {
if (__ct_state() == state) {
if (ct->active) {
/*
* Exit RCU idle mode while entering the kernel because it can
* run a RCU read side critical section anytime.
*/
rcu_eqs_exit(true);
ct_kernel_enter(true, RCU_DYNTICKS_IDX - state);
if (state == CONTEXT_USER) {
instrumentation_begin();
vtime_user_exit(current);
trace_user_exit(0);
instrumentation_end();
}
/*
* Special case if we only track user <-> kernel transitions for tickless
* cputime accounting but we don't support RCU extended quiescent state.
* In this we case we don't care about any concurrency/ordering.
*/
if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE))
atomic_set(&ct->state, CONTEXT_KERNEL);
} else {
if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
/* Tracking for vtime only, no concurrent RCU EQS accounting */
atomic_set(&ct->state, CONTEXT_KERNEL);
} else {
/*
* Tracking for vtime and RCU EQS. Make sure we don't race
* with NMIs. OTOH we don't care about ordering here since
* RCU only requires RCU_DYNTICKS_IDX increments to be fully
* ordered.
*/
atomic_sub(state, &ct->state);
}
}
__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
}

13
kernel/rcu/tree.c
View File

@ -272,9 +272,9 @@ void rcu_softirq_qs(void)
*/
static void rcu_dynticks_eqs_online(void)
{
if (ct_dynticks() & 0x1)
if (ct_dynticks() & RCU_DYNTICKS_IDX)
return;
rcu_dynticks_inc(1);
ct_state_inc(RCU_DYNTICKS_IDX);
}
/*
@ -293,7 +293,7 @@ static int rcu_dynticks_snap(int cpu)
*/
static bool rcu_dynticks_in_eqs(int snap)
{
return !(snap & 0x1);
return !(snap & RCU_DYNTICKS_IDX);
}
/* Return true if the specified CPU is currently idle from an RCU viewpoint. */
@ -321,8 +321,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
int snap;
// If not quiescent, force back to earlier extended quiescent state.
snap = ct_dynticks_cpu(cpu) & ~0x1;
snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
smp_rmb(); // Order ->dynticks and *vp reads.
if (READ_ONCE(*vp))
return false; // Non-zero, so report failure;
@ -348,9 +347,9 @@ notrace void rcu_momentary_dyntick_idle(void)
int seq;
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
seq = rcu_dynticks_inc(2);
seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
/* It is illegal to call this from idle state. */
WARN_ON_ONCE(!(seq & 0x1));
WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
rcu_preempt_deferred_qs(current);
}
EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);

4
kernel/rcu/tree_stall.h
View File

@ -469,7 +469,7 @@ static void print_cpu_stall_info(int cpu)
rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
if (rcuc_starved)
sprintf(buf, " rcuc=%ld jiffies(starved)", j);
pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
cpu,
"O."[!!cpu_online(cpu)],
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
@ -478,7 +478,7 @@ static void print_cpu_stall_info(int cpu)
rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
"!."[!delta],
ticks_value, ticks_title,
rcu_dynticks_snap(cpu) & 0xfff,
rcu_dynticks_snap(cpu) & 0xffff,
ct_dynticks_nesting_cpu(cpu), ct_dynticks_nmi_nesting_cpu(cpu),
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,