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Subject[PATCH tip/core/rcu 10/11] rcu: Provide wrappers for uses of ->rcu_read_lock_nesting
Date
From: Lai Jiangshan <laijs@linux.alibaba.com>

This commit provides wrapper functions for uses of ->rcu_read_lock_nesting
to improve readability and to ease future changes to support inlining
of __rcu_read_lock() and __rcu_read_unlock().

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_exp.h | 4 ++--
kernel/rcu/tree_plugin.h | 53 +++++++++++++++++++++++++++++++-----------------
2 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 98d078c..d8da6b1 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -610,7 +610,7 @@ static void rcu_exp_handler(void *unused)
* critical section. If also enabled or idle, immediately
* report the quiescent state, otherwise defer.
*/
- if (!t->rcu_read_lock_nesting) {
+ if (!rcu_preempt_depth()) {
if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
rcu_dynticks_curr_cpu_in_eqs()) {
rcu_report_exp_rdp(rdp);
@@ -634,7 +634,7 @@ static void rcu_exp_handler(void *unused)
* can have caused this quiescent state to already have been
* reported, so we really do need to check ->expmask.
*/
- if (t->rcu_read_lock_nesting > 0) {
+ if (rcu_preempt_depth() > 0) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->expmask & rdp->grpmask) {
rdp->exp_deferred_qs = true;
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 698a7f1..ebdbdec 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -290,8 +290,8 @@ void rcu_note_context_switch(bool preempt)

trace_rcu_utilization(TPS("Start context switch"));
lockdep_assert_irqs_disabled();
- WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
- if (t->rcu_read_lock_nesting > 0 &&
+ WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
+ if (rcu_preempt_depth() > 0 &&
!t->rcu_read_unlock_special.b.blocked) {

/* Possibly blocking in an RCU read-side critical section. */
@@ -348,6 +348,21 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
#define RCU_NEST_NMAX (-INT_MAX / 2)
#define RCU_NEST_PMAX (INT_MAX / 2)

+static void rcu_preempt_read_enter(void)
+{
+ current->rcu_read_lock_nesting++;
+}
+
+static void rcu_preempt_read_exit(void)
+{
+ current->rcu_read_lock_nesting--;
+}
+
+static void rcu_preempt_depth_set(int val)
+{
+ current->rcu_read_lock_nesting = val;
+}
+
/*
* Preemptible RCU implementation for rcu_read_lock().
* Just increment ->rcu_read_lock_nesting, shared state will be updated
@@ -355,9 +370,9 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
*/
void __rcu_read_lock(void)
{
- current->rcu_read_lock_nesting++;
+ rcu_preempt_read_enter();
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
- WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX);
+ WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
barrier(); /* critical section after entry code. */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -373,19 +388,19 @@ void __rcu_read_unlock(void)
{
struct task_struct *t = current;

- if (t->rcu_read_lock_nesting != 1) {
- --t->rcu_read_lock_nesting;
+ if (rcu_preempt_depth() != 1) {
+ rcu_preempt_read_exit();
} else {
barrier(); /* critical section before exit code. */
- t->rcu_read_lock_nesting = -RCU_NEST_BIAS;
+ rcu_preempt_depth_set(-RCU_NEST_BIAS);
barrier(); /* assign before ->rcu_read_unlock_special load */
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
rcu_read_unlock_special(t);
barrier(); /* ->rcu_read_unlock_special load before assign */
- t->rcu_read_lock_nesting = 0;
+ rcu_preempt_depth_set(0);
}
if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
- int rrln = t->rcu_read_lock_nesting;
+ int rrln = rcu_preempt_depth();

WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
}
@@ -539,7 +554,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
READ_ONCE(t->rcu_read_unlock_special.s)) &&
- t->rcu_read_lock_nesting <= 0;
+ rcu_preempt_depth() <= 0;
}

/*
@@ -552,16 +567,16 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
static void rcu_preempt_deferred_qs(struct task_struct *t)
{
unsigned long flags;
- bool couldrecurse = t->rcu_read_lock_nesting >= 0;
+ bool couldrecurse = rcu_preempt_depth() >= 0;

if (!rcu_preempt_need_deferred_qs(t))
return;
if (couldrecurse)
- t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
+ rcu_preempt_depth_set(rcu_preempt_depth() - RCU_NEST_BIAS);
local_irq_save(flags);
rcu_preempt_deferred_qs_irqrestore(t, flags);
if (couldrecurse)
- t->rcu_read_lock_nesting += RCU_NEST_BIAS;
+ rcu_preempt_depth_set(rcu_preempt_depth() + RCU_NEST_BIAS);
}

/*
@@ -672,7 +687,7 @@ static void rcu_flavor_sched_clock_irq(int user)
if (user || rcu_is_cpu_rrupt_from_idle()) {
rcu_note_voluntary_context_switch(current);
}
- if (t->rcu_read_lock_nesting > 0 ||
+ if (rcu_preempt_depth() > 0 ||
(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
/* No QS, force context switch if deferred. */
if (rcu_preempt_need_deferred_qs(t)) {
@@ -682,13 +697,13 @@ static void rcu_flavor_sched_clock_irq(int user)
} else if (rcu_preempt_need_deferred_qs(t)) {
rcu_preempt_deferred_qs(t); /* Report deferred QS. */
return;
- } else if (!t->rcu_read_lock_nesting) {
+ } else if (!rcu_preempt_depth()) {
rcu_qs(); /* Report immediate QS. */
return;
}

/* If GP is oldish, ask for help from rcu_read_unlock_special(). */
- if (t->rcu_read_lock_nesting > 0 &&
+ if (rcu_preempt_depth() > 0 &&
__this_cpu_read(rcu_data.core_needs_qs) &&
__this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
!t->rcu_read_unlock_special.b.need_qs &&
@@ -709,11 +724,11 @@ void exit_rcu(void)
struct task_struct *t = current;

if (unlikely(!list_empty(&current->rcu_node_entry))) {
- t->rcu_read_lock_nesting = 1;
+ rcu_preempt_depth_set(1);
barrier();
WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
- } else if (unlikely(t->rcu_read_lock_nesting)) {
- t->rcu_read_lock_nesting = 1;
+ } else if (unlikely(rcu_preempt_depth())) {
+ rcu_preempt_depth_set(1);
} else {
return;
}
--
2.9.5
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