[PATCH 10/19] rcu/context_tracking: Move dynticks counter to context tracking

From: Frederic Weisbecker
Date: Wed Mar 02 2022 - 10:50:00 EST

In order to prepare for merging RCU dynticks counter into the context
tracking state, move the rcu_data's dynticks field to the context
tracking structure. It will later be mixed within the context tracking
state itself.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
Cc: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
Cc: Yu Liao<liaoyu15@xxxxxxxxxx>
Cc: Phil Auld <pauld@xxxxxxxxxx>
Cc: Paul Gortmaker<paul.gortmaker@xxxxxxxxxxxxx>
Cc: Alex Belits <abelits@xxxxxxxxxxx>
---
include/linux/context_tracking_state.h | 10 ++++-
kernel/context_tracking.c | 9 ++--
kernel/rcu/tree.c | 59 ++++++++++++++------------
kernel/rcu/tree.h | 1 -
kernel/rcu/tree_exp.h | 2 +-
kernel/rcu/tree_stall.h | 4 +-
6 files changed, 48 insertions(+), 37 deletions(-)

diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index cdc692caa01d..5ad0e481c5a3 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -7,6 +7,7 @@
#include <linux/context_tracking_irq.h>

struct context_tracking {
+#ifdef CONFIG_CONTEXT_TRACKING_USER
/*
* When active is false, probes are unset in order
* to minimize overhead: TIF flags are cleared
@@ -21,11 +22,16 @@ struct context_tracking {
CONTEXT_USER,
CONTEXT_GUEST,
} state;
+#endif
+ atomic_t dynticks; /* Even value for idle, else odd. */
};

-#ifdef CONFIG_CONTEXT_TRACKING_USER
-extern struct static_key_false context_tracking_key;
+#ifdef CONFIG_CONTEXT_TRACKING
DECLARE_PER_CPU(struct context_tracking, context_tracking);
+#endif
+
+#ifdef CONFIG_CONTEXT_TRACKING_USER
+extern struct static_key_false context_tracking_key;

static __always_inline bool context_tracking_enabled(void)
{
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index ea22eb04750f..77b61a7c9890 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -30,9 +30,6 @@
DEFINE_STATIC_KEY_FALSE(context_tracking_key);
EXPORT_SYMBOL_GPL(context_tracking_key);

-DEFINE_PER_CPU(struct context_tracking, context_tracking);
-EXPORT_SYMBOL_GPL(context_tracking);
-
static noinstr bool context_tracking_recursion_enter(void)
{
int recursion;
@@ -236,6 +233,12 @@ void __init context_tracking_init(void)

#endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */

+DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
+ .dynticks = ATOMIC_INIT(1),
+};
+EXPORT_SYMBOL_GPL(context_tracking);
+
+
void ct_idle_enter(void)
{
rcu_idle_enter();
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cadf5f5a4700..96eb8503f28e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -77,7 +77,6 @@
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
- .dynticks = ATOMIC_INIT(1),
#ifdef CONFIG_RCU_NOCB_CPU
.cblist.flags = SEGCBLIST_RCU_CORE,
#endif
@@ -268,7 +267,7 @@ void rcu_softirq_qs(void)
*/
static noinline noinstr unsigned long rcu_dynticks_inc(int incby)
{
- return arch_atomic_add_return(incby, this_cpu_ptr(&rcu_data.dynticks));
+ return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.dynticks));
}

/*
@@ -324,9 +323,9 @@ static noinstr void rcu_dynticks_eqs_exit(void)
*/
static void rcu_dynticks_eqs_online(void)
{
- struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);

- if (atomic_read(&rdp->dynticks) & 0x1)
+ if (atomic_read(&ct->dynticks) & 0x1)
return;
rcu_dynticks_inc(1);
}
@@ -338,17 +337,19 @@ static void rcu_dynticks_eqs_online(void)
*/
static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
{
- return !(arch_atomic_read(this_cpu_ptr(&rcu_data.dynticks)) & 0x1);
+ return !(arch_atomic_read(this_cpu_ptr(&context_tracking.dynticks)) & 0x1);
}

/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
-static int rcu_dynticks_snap(struct rcu_data *rdp)
+static int rcu_dynticks_snap(int cpu)
{
+ struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
+
smp_mb(); // Fundamental RCU ordering guarantee.
- return atomic_read_acquire(&rdp->dynticks);
+ return atomic_read_acquire(&ct->dynticks);
}

/*
@@ -363,9 +364,7 @@ static bool rcu_dynticks_in_eqs(int snap)
/* Return true if the specified CPU is currently idle from an RCU viewpoint. */
bool rcu_is_idle_cpu(int cpu)
{
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
-
- return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
+ return rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
}

/*
@@ -375,7 +374,7 @@ bool rcu_is_idle_cpu(int cpu)
*/
static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
{
- return snap != rcu_dynticks_snap(rdp);
+ return snap != rcu_dynticks_snap(rdp->cpu);
}

/*
@@ -384,11 +383,11 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
*/
bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
{
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
int snap;

// If not quiescent, force back to earlier extended quiescent state.
- snap = atomic_read(&rdp->dynticks) & ~0x1;
+ snap = atomic_read(&ct->dynticks) & ~0x1;

smp_rmb(); // Order ->dynticks and *vp reads.
if (READ_ONCE(*vp))
@@ -396,7 +395,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
smp_rmb(); // Order *vp read and ->dynticks re-read.

// If still in the same extended quiescent state, we are good!
- return snap == atomic_read(&rdp->dynticks);
+ return snap == atomic_read(&ct->dynticks);
}

/*
@@ -620,6 +619,7 @@ EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
static noinstr void rcu_eqs_enter(bool user)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);

WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
@@ -633,12 +633,12 @@ static noinstr void rcu_eqs_enter(bool user)

lockdep_assert_irqs_disabled();
instrumentation_begin();
- trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&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 rcu_dynticks_eqs_enter()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+ instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));

instrumentation_end();
WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
@@ -740,7 +740,7 @@ noinstr void rcu_user_enter(void)
* rcu_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 rdp->dynticks and rdp->dynticks_nmi_nesting
+ * RCU-idle period, update ct->dynticks and rdp->dynticks_nmi_nesting
* to let the RCU grace-period handling know that the CPU is back to
* being RCU-idle.
*
@@ -749,6 +749,7 @@ noinstr void rcu_user_enter(void)
*/
noinstr void rcu_nmi_exit(void)
{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);

instrumentation_begin();
@@ -766,7 +767,7 @@ noinstr void rcu_nmi_exit(void)
*/
if (rdp->dynticks_nmi_nesting != 1) {
trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
- atomic_read(&rdp->dynticks));
+ atomic_read(&ct->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
instrumentation_end();
@@ -774,11 +775,11 @@ noinstr void rcu_nmi_exit(void)
}

/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
- trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&ct->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */

// instrumentation for the noinstr rcu_dynticks_eqs_enter()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+ instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
instrumentation_end();

// RCU is watching here ...
@@ -817,6 +818,7 @@ void rcu_irq_exit_check_preempt(void)
*/
static void noinstr rcu_eqs_exit(bool user)
{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
struct rcu_data *rdp;
long oldval;

@@ -836,9 +838,9 @@ static void noinstr rcu_eqs_exit(bool user)
instrumentation_begin();

// instrumentation for the noinstr rcu_dynticks_eqs_exit()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+ instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));

- trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
+ trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&ct->dynticks));
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
WRITE_ONCE(rdp->dynticks_nesting, 1);
WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
@@ -944,7 +946,7 @@ void __rcu_irq_enter_check_tick(void)
/**
* rcu_nmi_enter - inform RCU of entry to NMI context
*
- * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
+ * If the CPU was idle from RCU's viewpoint, update ct->dynticks and
* rdp->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
@@ -957,6 +959,7 @@ noinstr void rcu_nmi_enter(void)
{
long incby = 2;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);

/* Complain about underflow. */
WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
@@ -980,9 +983,9 @@ noinstr void rcu_nmi_enter(void)

instrumentation_begin();
// instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
- instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
+ instrument_atomic_read(&ct->dynticks, sizeof(ct->dynticks));
// instrumentation for the noinstr rcu_dynticks_eqs_exit()
- instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
+ instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));

incby = 1;
} else if (!in_nmi()) {
@@ -994,7 +997,7 @@ noinstr void rcu_nmi_enter(void)

trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
rdp->dynticks_nmi_nesting,
- rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
+ rdp->dynticks_nmi_nesting + incby, atomic_read(&ct->dynticks));
instrumentation_end();
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
rdp->dynticks_nmi_nesting + incby);
@@ -1138,7 +1141,7 @@ static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
- rdp->dynticks_snap = rcu_dynticks_snap(rdp);
+ rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
rcu_gpnum_ovf(rdp->mynode, rdp);
@@ -4125,7 +4128,7 @@ rcu_boot_init_percpu_data(int cpu)
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
INIT_WORK(&rdp->strict_work, strict_work_handler);
WARN_ON_ONCE(rdp->dynticks_nesting != 1);
- WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
+ WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
rdp->barrier_seq_snap = rcu_state.barrier_sequence;
rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index b8d07bf92d29..15246a3f0734 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -188,7 +188,6 @@ struct rcu_data {
int dynticks_snap; /* Per-GP tracking for dynticks. */
long dynticks_nesting; /* Track process nesting level. */
long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
- atomic_t dynticks; /* Even value for idle, else odd. */
bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
bool rcu_urgent_qs; /* GP old need light quiescent state. */
bool rcu_forced_tick; /* Forced tick to provide QS. */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index d5f30085b0cf..2210110990f4 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -358,7 +358,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
!(rnp->qsmaskinitnext & mask)) {
mask_ofl_test |= mask;
} else {
- snap = rcu_dynticks_snap(rdp);
+ snap = rcu_dynticks_snap(cpu);
if (rcu_dynticks_in_eqs(snap))
mask_ofl_test |= mask;
else
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 84b812a3ab44..202129b1c7e4 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -448,7 +448,7 @@ static void print_cpu_stall_info(int cpu)
}
delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
falsepositive = rcu_is_gp_kthread_starving(NULL) &&
- rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
+ rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
cpu,
"O."[!!cpu_online(cpu)],
@@ -458,7 +458,7 @@ 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(rdp) & 0xfff,
+ rcu_dynticks_snap(cpu) & 0xfff,
rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
--
2.25.1