[PATCH] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"

From: Ingo Molnar
Date: Thu May 12 2011 - 02:02:05 EST

This reverts commit e59fb3120becfb36b22ddb8bd27d065d3cdca499.

Conflicts:

Documentation/RCU/trace.txt
kernel/rcutree.c
---
Documentation/RCU/trace.txt | 78 ++++++++++++--------------
kernel/rcutree.c | 130 ++++++++++++++++++++++++------------------
kernel/rcutree.h | 9 ++-
kernel/rcutree_plugin.h | 7 +-
kernel/rcutree_trace.c | 12 ++--
5 files changed, 126 insertions(+), 110 deletions(-)

diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 8173cec..2b4d887 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -10,46 +10,34 @@ for rcutree and next for rcutiny.

CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats

-These implementations of RCU provides several debugfs files under the
-top-level directory "rcu":
-
-rcu/rcudata:
- Displays fields in struct rcu_data.
-rcu/rcudata.csv:
- Comma-separated values spreadsheet version of rcudata.
-rcu/rcugp:
- Displays grace-period counters.
-rcu/rcuhier:
- Displays the struct rcu_node hierarchy.
-rcu/rcu_pending:
- Displays counts of the reasons rcu_pending() decided that RCU had
- work to do.
-rcu/rcutorture:
- Displays rcutorture test progress.
-rcu/rcuboost:
- Displays RCU boosting statistics. Only present if
- CONFIG_RCU_BOOST=y.
+These implementations of RCU provides five debugfs files under the
+top-level directory RCU: rcu/rcudata (which displays fields in struct
+rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of
+rcu/rcudata), rcu/rcugp (which displays grace-period counters),
+rcu/rcuhier (which displays the struct rcu_node hierarchy), and
+rcu/rcu_pending (which displays counts of the reasons that the
+rcu_pending() function decided that there was core RCU work to do).

The output of "cat rcu/rcudata" looks as follows:

rcu_sched:
- 0 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=545/1/0 df=50 of=0 ri=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
- 1 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=967/1/0 df=58 of=0 ri=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
- 2 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=1081/1/0 df=175 of=0 ri=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
- 3 c=20942 g=20943 pq=1 pqc=20942 qp=1 dt=1846/0/0 df=404 of=0 ri=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
- 4 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=369/1/0 df=83 of=0 ri=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
- 5 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=381/1/0 df=64 of=0 ri=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
- 6 c=20972 g=20973 pq=1 pqc=20972 qp=0 dt=1037/1/0 df=183 of=0 ri=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
- 7 c=20897 g=20897 pq=1 pqc=20896 qp=0 dt=1572/0/0 df=382 of=0 ri=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
+ 0 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=10951/1 dn=0 df=1101 of=0 ri=36 ql=0 b=10
+ 1 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=16117/1 dn=0 df=1015 of=0 ri=0 ql=0 b=10
+ 2 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1445/1 dn=0 df=1839 of=0 ri=0 ql=0 b=10
+ 3 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=6681/1 dn=0 df=1545 of=0 ri=0 ql=0 b=10
+ 4 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1003/1 dn=0 df=1992 of=0 ri=0 ql=0 b=10
+ 5 c=17829 g=17830 pq=1 pqc=17829 qp=1 dt=3887/1 dn=0 df=3331 of=0 ri=4 ql=2 b=10
+ 6 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=859/1 dn=0 df=3224 of=0 ri=0 ql=0 b=10
+ 7 c=17829 g=17830 pq=0 pqc=17829 qp=1 dt=3761/1 dn=0 df=1818 of=0 ri=0 ql=2 b=10
rcu_bh:
- 0 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=545/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
- 1 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=967/1/0 df=3 of=0 ri=1 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
- 2 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1081/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
- 3 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1846/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
- 4 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=369/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
- 5 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=381/1/0 df=4 of=0 ri=1 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
- 6 c=1480 g=1480 pq=1 pqc=1479 qp=0 dt=1037/1/0 df=6 of=0 ri=1 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
- 7 c=1474 g=1474 pq=1 pqc=1473 qp=0 dt=1572/0/0 df=8 of=0 ri=1 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0
+ 0 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=10951/1 dn=0 df=0 of=0 ri=0 ql=0 b=10
+ 1 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=16117/1 dn=0 df=13 of=0 ri=0 ql=0 b=10
+ 2 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1445/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
+ 3 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=6681/1 dn=0 df=9 of=0 ri=0 ql=0 b=10
+ 4 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1003/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
+ 5 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3887/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
+ 6 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=859/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
+ 7 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3761/1 dn=0 df=15 of=0 ri=0 ql=0 b=10

The first section lists the rcu_data structures for rcu_sched, the second
for rcu_bh. Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
@@ -94,16 +82,22 @@ o "pqc" indicates which grace period the last-observed quiescent
the next grace period!

o "qp" indicates that RCU still expects a quiescent state from
- this CPU. Offlined CPUs and CPUs in dyntick idle mode might
- well have qp=1, which is OK: RCU is still ignoring them.
+ this CPU.

o "dt" is the current value of the dyntick counter that is incremented
when entering or leaving dynticks idle state, either by the
- scheduler or by irq. This number is even if the CPU is in
- dyntick idle mode and odd otherwise. The number after the first
- "/" is the interrupt nesting depth when in dyntick-idle state,
- or one greater than the interrupt-nesting depth otherwise.
- The number after the second "/" is the NMI nesting depth.
+ scheduler or by irq. The number after the "/" is the interrupt
+ nesting depth when in dyntick-idle state, or one greater than
+ the interrupt-nesting depth otherwise.
+
+ This field is displayed only for CONFIG_NO_HZ kernels.
+
+o "dn" is the current value of the dyntick counter that is incremented
+ when entering or leaving dynticks idle state via NMI. If both
+ the "dt" and "dn" values are even, then this CPU is in dynticks
+ idle mode and may be ignored by RCU. If either of these two
+ counters is odd, then RCU must be alert to the possibility of
+ an RCU read-side critical section running on this CPU.

This field is displayed only for CONFIG_NO_HZ kernels.

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 5616b17..e486f7c 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -162,7 +162,7 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
#ifdef CONFIG_NO_HZ
DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = 1,
- .dynticks = ATOMIC_INIT(1),
+ .dynticks = 1,
};
#endif /* #ifdef CONFIG_NO_HZ */

@@ -321,25 +321,13 @@ void rcu_enter_nohz(void)
unsigned long flags;
struct rcu_dynticks *rdtp;

+ smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
- if (--rdtp->dynticks_nesting) {
- local_irq_restore(flags);
- return;
- }
- /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
- smp_mb__before_atomic_inc(); /* See above. */
- atomic_inc(&rdtp->dynticks);
- smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
- WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+ rdtp->dynticks++;
+ rdtp->dynticks_nesting--;
+ WARN_ON_ONCE(rdtp->dynticks & 0x1);
local_irq_restore(flags);
-
- /* If the interrupt queued a callback, get out of dyntick mode. */
- if (in_irq() &&
- (__get_cpu_var(rcu_sched_data).nxtlist ||
- __get_cpu_var(rcu_bh_data).nxtlist ||
- rcu_preempt_needs_cpu(smp_processor_id())))
- set_need_resched();
}

/*
@@ -355,16 +343,11 @@ void rcu_exit_nohz(void)

local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
- if (rdtp->dynticks_nesting++) {
- local_irq_restore(flags);
- return;
- }
- smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
- atomic_inc(&rdtp->dynticks);
- /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
- smp_mb__after_atomic_inc(); /* See above. */
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ rdtp->dynticks++;
+ rdtp->dynticks_nesting++;
+ WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
local_irq_restore(flags);
+ smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
@@ -378,15 +361,11 @@ void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

- if (rdtp->dynticks_nmi_nesting == 0 &&
- (atomic_read(&rdtp->dynticks) & 0x1))
+ if (rdtp->dynticks & 0x1)
return;
- rdtp->dynticks_nmi_nesting++;
- smp_mb__before_atomic_inc(); /* Force delay from prior write. */
- atomic_inc(&rdtp->dynticks);
- /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
- smp_mb__after_atomic_inc(); /* See above. */
- WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
+ rdtp->dynticks_nmi++;
+ WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
+ smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
@@ -400,14 +379,11 @@ void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);

- if (rdtp->dynticks_nmi_nesting == 0 ||
- --rdtp->dynticks_nmi_nesting != 0)
+ if (rdtp->dynticks & 0x1)
return;
- /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
- smp_mb__before_atomic_inc(); /* See above. */
- atomic_inc(&rdtp->dynticks);
- smp_mb__after_atomic_inc(); /* Force delay to next write. */
- WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
+ smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
+ rdtp->dynticks_nmi++;
+ WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
}

/**
@@ -418,7 +394,13 @@ void rcu_nmi_exit(void)
*/
void rcu_irq_enter(void)
{
- rcu_exit_nohz();
+ struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
+
+ if (rdtp->dynticks_nesting++)
+ return;
+ rdtp->dynticks++;
+ WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
+ smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
}

/**
@@ -430,7 +412,18 @@ void rcu_irq_enter(void)
*/
void rcu_irq_exit(void)
{
- rcu_enter_nohz();
+ struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
+
+ if (--rdtp->dynticks_nesting)
+ return;
+ smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
+ rdtp->dynticks++;
+ WARN_ON_ONCE(rdtp->dynticks & 0x1);
+
+ /* If the interrupt queued a callback, get out of dyntick mode. */
+ if (__this_cpu_read(rcu_sched_data.nxtlist) ||
+ __this_cpu_read(rcu_bh_data.nxtlist))
+ set_need_resched();
}

#ifdef CONFIG_SMP
@@ -442,8 +435,19 @@ void rcu_irq_exit(void)
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
- rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
- return 0;
+ int ret;
+ int snap;
+ int snap_nmi;
+
+ snap = rdp->dynticks->dynticks;
+ snap_nmi = rdp->dynticks->dynticks_nmi;
+ smp_mb(); /* Order sampling of snap with end of grace period. */
+ rdp->dynticks_snap = snap;
+ rdp->dynticks_nmi_snap = snap_nmi;
+ ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
+ if (ret)
+ rdp->dynticks_fqs++;
+ return ret;
}

/*
@@ -454,11 +458,16 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
{
- unsigned long curr;
- unsigned long snap;
+ long curr;
+ long curr_nmi;
+ long snap;
+ long snap_nmi;

- curr = (unsigned long)atomic_add_return(0, &rdp->dynticks->dynticks);
- snap = (unsigned long)rdp->dynticks_snap;
+ curr = rdp->dynticks->dynticks;
+ snap = rdp->dynticks_snap;
+ curr_nmi = rdp->dynticks->dynticks_nmi;
+ snap_nmi = rdp->dynticks_nmi_snap;
+ smp_mb(); /* force ordering with cpu entering/leaving dynticks. */

/*
* If the CPU passed through or entered a dynticks idle phase with
@@ -468,7 +477,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
- if ((curr & 0x1) == 0 || ULONG_CMP_GE(curr, snap + 2)) {
+ if ((curr != snap || (curr & 0x1) == 0) &&
+ (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
rdp->dynticks_fqs++;
return 1;
}
@@ -897,12 +907,6 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
unsigned long gp_duration;

WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
-
- /*
- * Ensure that all grace-period and pre-grace-period activity
- * is seen before the assignment to rsp->completed.
- */
- smp_mb(); /* See above block comment. */
gp_duration = jiffies - rsp->gp_start;
if (gp_duration > rsp->gp_max)
rsp->gp_max = gp_duration;
@@ -1450,11 +1454,25 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
*/
static void rcu_process_callbacks(void)
{
+ /*
+ * Memory references from any prior RCU read-side critical sections
+ * executed by the interrupted code must be seen before any RCU
+ * grace-period manipulations below.
+ */
+ smp_mb(); /* See above block comment. */
+
__rcu_process_callbacks(&rcu_sched_state,
&__get_cpu_var(rcu_sched_data));
__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
rcu_preempt_process_callbacks();

+ /*
+ * Memory references from any later RCU read-side critical sections
+ * executed by the interrupted code must be seen after any RCU
+ * grace-period manipulations above.
+ */
+ smp_mb(); /* See above block comment. */
+
/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
rcu_needs_cpu_flush();
}
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 93d4a1c..2576648 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -84,9 +84,11 @@
* Dynticks per-CPU state.
*/
struct rcu_dynticks {
- int dynticks_nesting; /* Track irq/process nesting level. */
- int dynticks_nmi_nesting; /* Track NMI nesting level. */
- atomic_t dynticks; /* Even value for dynticks-idle, else odd. */
+ int dynticks_nesting; /* Track nesting level, sort of. */
+ int dynticks; /* Even value for dynticks-idle, else odd. */
+ int dynticks_nmi; /* Even value for either dynticks-idle or */
+ /* not in nmi handler, else odd. So this */
+ /* remains even for nmi from irq handler. */
};

/* RCU's kthread states for tracing. */
@@ -282,6 +284,7 @@ struct rcu_data {
/* 3) dynticks interface. */
struct rcu_dynticks *dynticks; /* Shared per-CPU dynticks state. */
int dynticks_snap; /* Per-GP tracking for dynticks. */
+ int dynticks_nmi_snap; /* Per-GP tracking for dynticks_nmi. */
#endif /* #ifdef CONFIG_NO_HZ */

/* 4) reasons this CPU needed to be kicked by force_quiescent_state */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index ed339702..3f6559a 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1520,6 +1520,7 @@ int rcu_needs_cpu(int cpu)
{
int c = 0;
int snap;
+ int snap_nmi;
int thatcpu;

/* Check for being in the holdoff period. */
@@ -1530,10 +1531,10 @@ int rcu_needs_cpu(int cpu)
for_each_online_cpu(thatcpu) {
if (thatcpu == cpu)
continue;
- snap = atomic_add_return(0, &per_cpu(rcu_dynticks,
- thatcpu).dynticks);
+ snap = per_cpu(rcu_dynticks, thatcpu).dynticks;
+ snap_nmi = per_cpu(rcu_dynticks, thatcpu).dynticks_nmi;
smp_mb(); /* Order sampling of snap with end of grace period. */
- if ((snap & 0x1) != 0) {
+ if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) {
per_cpu(rcu_dyntick_drain, cpu) = 0;
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
return rcu_needs_cpu_quick_check(cpu);
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 9678cc3..aa0fd72 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -69,10 +69,10 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->passed_quiesc, rdp->passed_quiesc_completed,
rdp->qs_pending);
#ifdef CONFIG_NO_HZ
- seq_printf(m, " dt=%d/%d/%d df=%lu",
- atomic_read(&rdp->dynticks->dynticks),
+ seq_printf(m, " dt=%d/%d dn=%d df=%lu",
+ rdp->dynticks->dynticks,
rdp->dynticks->dynticks_nesting,
- rdp->dynticks->dynticks_nmi_nesting,
+ rdp->dynticks->dynticks_nmi,
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
@@ -141,9 +141,9 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->qs_pending);
#ifdef CONFIG_NO_HZ
seq_printf(m, ",%d,%d,%d,%lu",
- atomic_read(&rdp->dynticks->dynticks),
+ rdp->dynticks->dynticks,
rdp->dynticks->dynticks_nesting,
- rdp->dynticks->dynticks_nmi_nesting,
+ rdp->dynticks->dynticks_nmi,
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
@@ -167,7 +167,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
{
seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pqc\",\"pq\",");
#ifdef CONFIG_NO_HZ
- seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
+ seq_puts(m, "\"dt\",\"dt nesting\",\"dn\",\"df\",");
#endif /* #ifdef CONFIG_NO_HZ */
seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n");
#ifdef CONFIG_TREE_PREEMPT_RCU
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