[PATCH 8/8] cputime: Safely read cputime of full dynticks CPUs

From: Frederic Weisbecker
Date: Tue Jan 22 2013 - 19:04:30 EST

While remotely reading the cputime of a task running in a
full dynticks CPU, the values stored in utime/stime fields
of struct task_struct may be stale. Its values may be those
of the last kernel <-> user transition time snapshot and
we need to add the tickless time spent since this snapshot.

To fix this, flush the cputime of the dynticks CPUs on
kernel <-> user transition and record the time / context
where we did this. Then on top of this snapshot and the current
time, perform the fixup on the reader side from task_times()
accessors.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/s390/kernel/vtime.c | 6 +-
include/linux/hardirq.h | 4 +-
include/linux/init_task.h | 11 +++
include/linux/kvm_host.h | 20 ++++-
include/linux/sched.h | 27 +++++-
include/linux/vtime.h | 47 +++++------
kernel/context_tracking.c | 19 +++++
kernel/fork.c | 6 ++
kernel/sched/core.c | 1 +
kernel/sched/cputime.c | 195 ++++++++++++++++++++++++++++++++++++++++++---
kernel/softirq.c | 6 +-
11 files changed, 291 insertions(+), 51 deletions(-)

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index e84b8b6..ce9cc5a 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -127,7 +127,7 @@ void vtime_account_user(struct task_struct *tsk)
* Update process times based on virtual cpu times stored by entry.S
* to the lowcore fields user_timer, system_timer & steal_clock.
*/
-void vtime_account(struct task_struct *tsk)
+void vtime_account_irq_enter(struct task_struct *tsk)
{
struct thread_info *ti = task_thread_info(tsk);
u64 timer, system;
@@ -145,10 +145,10 @@ void vtime_account(struct task_struct *tsk)

virt_timer_forward(system);
}
-EXPORT_SYMBOL_GPL(vtime_account);
+EXPORT_SYMBOL_GPL(vtime_account_irq_enter);

void vtime_account_system(struct task_struct *tsk)
-__attribute__((alias("vtime_account")));
+__attribute__((alias("vtime_account_irq_enter")));
EXPORT_SYMBOL_GPL(vtime_account_system);

void __kprobes vtime_stop_cpu(void)
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 624ef3f..7105d5c 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -153,7 +153,7 @@ extern void rcu_nmi_exit(void);
*/
#define __irq_enter() \
do { \
- vtime_account_irq_enter(current); \
+ account_irq_enter_time(current); \
add_preempt_count(HARDIRQ_OFFSET); \
trace_hardirq_enter(); \
} while (0)
@@ -169,7 +169,7 @@ extern void irq_enter(void);
#define __irq_exit() \
do { \
trace_hardirq_exit(); \
- vtime_account_irq_exit(current); \
+ account_irq_exit_time(current); \
sub_preempt_count(HARDIRQ_OFFSET); \
} while (0)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6d087c5..cc898b8 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -10,6 +10,7 @@
#include <linux/pid_namespace.h>
#include <linux/user_namespace.h>
#include <linux/securebits.h>
+#include <linux/seqlock.h>
#include <net/net_namespace.h>

#ifdef CONFIG_SMP
@@ -141,6 +142,15 @@ extern struct task_group root_task_group;
# define INIT_PERF_EVENTS(tsk)
#endif

+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+# define INIT_VTIME(tsk) \
+ .vtime_seqlock = __SEQLOCK_UNLOCKED(tsk.vtime_seqlock), \
+ .vtime_snap = 0, \
+ .vtime_snap_whence = VTIME_SYS,
+#else
+# define INIT_VTIME(tsk)
+#endif
+
#define INIT_TASK_COMM "swapper"

/*
@@ -210,6 +220,7 @@ extern struct task_group root_task_group;
INIT_TRACE_RECURSION \
INIT_TASK_RCU_PREEMPT(tsk) \
INIT_CPUSET_SEQ \
+ INIT_VTIME(tsk) \
}


diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4fe2396..b7996a7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -741,7 +741,7 @@ static inline int kvm_deassign_device(struct kvm *kvm,
}
#endif /* CONFIG_IOMMU_API */

-static inline void guest_enter(void)
+static inline void __guest_enter(void)
{
/*
* This is running in ioctl context so we can avoid
@@ -751,7 +751,7 @@ static inline void guest_enter(void)
current->flags |= PF_VCPU;
}

-static inline void guest_exit(void)
+static inline void __guest_exit(void)
{
/*
* This is running in ioctl context so we can avoid
@@ -761,6 +761,22 @@ static inline void guest_exit(void)
current->flags &= ~PF_VCPU;
}

+#ifdef CONFIG_CONTEXT_TRACKING
+extern void guest_enter(void);
+extern void guest_exit(void);
+
+#else /* !CONFIG_CONTEXT_TRACKING */
+static inline void guest_enter(void)
+{
+ __guest_enter();
+}
+
+static inline void guest_exit(void)
+{
+ __guest_exit();
+}
+#endif /* !CONFIG_CONTEXT_TRACKING */
+
static inline void kvm_guest_enter(void)
{
unsigned long flags;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a9c608b..a9fa514 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1368,6 +1368,15 @@ struct task_struct {
#ifndef CONFIG_VIRT_CPU_ACCOUNTING
struct cputime prev_cputime;
#endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+ seqlock_t vtime_seqlock;
+ unsigned long long vtime_snap;
+ enum {
+ VTIME_SLEEPING = 0,
+ VTIME_USER,
+ VTIME_SYS,
+ } vtime_snap_whence;
+#endif
unsigned long nvcsw, nivcsw; /* context switch counts */
struct timespec start_time; /* monotonic time */
struct timespec real_start_time; /* boot based time */
@@ -1792,11 +1801,13 @@ static inline void put_task_struct(struct task_struct *t)
__put_task_struct(t);
}

-static inline cputime_t task_gtime(struct task_struct *t)
-{
- return t->gtime;
-}
-
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+extern void task_cputime(struct task_struct *t,
+ cputime_t *utime, cputime_t *stime);
+extern void task_cputime_scaled(struct task_struct *t,
+ cputime_t *utimescaled, cputime_t *stimescaled);
+extern cputime_t task_gtime(struct task_struct *t);
+#else
static inline void task_cputime(struct task_struct *t,
cputime_t *utime, cputime_t *stime)
{
@@ -1815,6 +1826,12 @@ static inline void task_cputime_scaled(struct task_struct *t,
if (stimescaled)
*stimescaled = t->stimescaled;
}
+
+static inline cputime_t task_gtime(struct task_struct *t)
+{
+ return t->gtime;
+}
+#endif
extern void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st);
extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st);

diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index bb50c3c..71a5782 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -8,35 +8,44 @@ extern void vtime_task_switch(struct task_struct *prev);
extern void vtime_account_system(struct task_struct *tsk);
extern void vtime_account_idle(struct task_struct *tsk);
extern void vtime_account_user(struct task_struct *tsk);
-extern void vtime_account(struct task_struct *tsk);
+extern void vtime_account_irq_enter(struct task_struct *tsk);

-#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-extern bool vtime_accounting_enabled(void);
-#else
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
static inline bool vtime_accounting_enabled(void) { return true; }
#endif

#else /* !CONFIG_VIRT_CPU_ACCOUNTING */
+
static inline void vtime_task_switch(struct task_struct *prev) { }
static inline void vtime_account_system(struct task_struct *tsk) { }
static inline void vtime_account_user(struct task_struct *tsk) { }
-static inline void vtime_account(struct task_struct *tsk) { }
+static inline void vtime_account_irq_enter(struct task_struct *tsk) { }
static inline bool vtime_accounting_enabled(void) { return false; }
#endif

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-static inline void arch_vtime_task_switch(struct task_struct *tsk) { }
-static inline void vtime_user_enter(struct task_struct *tsk)
-{
- vtime_account_system(tsk);
-}
+extern void arch_vtime_task_switch(struct task_struct *tsk);
+extern void vtime_account_irq_exit(struct task_struct *tsk);
+extern bool vtime_accounting_enabled(void);
+extern void vtime_user_enter(struct task_struct *tsk);
static inline void vtime_user_exit(struct task_struct *tsk)
{
vtime_account_user(tsk);
}
+extern void vtime_guest_enter(struct task_struct *tsk);
+extern void vtime_guest_exit(struct task_struct *tsk);
+extern void vtime_init_idle(struct task_struct *tsk);
#else
+static inline void vtime_account_irq_exit(struct task_struct *tsk)
+{
+ /* On hard|softirq exit we always account to hard|softirq cputime */
+ vtime_account_system(tsk);
+}
static inline void vtime_user_enter(struct task_struct *tsk) { }
static inline void vtime_user_exit(struct task_struct *tsk) { }
+static inline void vtime_guest_enter(struct task_struct *tsk) { }
+static inline void vtime_guest_exit(struct task_struct *tsk) { }
+static inline void vtime_init_idle(struct task_struct *tsk) { }
#endif

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
@@ -45,25 +54,15 @@ extern void irqtime_account_irq(struct task_struct *tsk);
static inline void irqtime_account_irq(struct task_struct *tsk) { }
#endif

-static inline void vtime_account_irq_enter(struct task_struct *tsk)
+static inline void account_irq_enter_time(struct task_struct *tsk)
{
- /*
- * Hardirq can interrupt idle task anytime. So we need vtime_account()
- * that performs the idle check in CONFIG_VIRT_CPU_ACCOUNTING.
- * Softirq can also interrupt idle task directly if it calls
- * local_bh_enable(). Such case probably don't exist but we never know.
- * Ksoftirqd is not concerned because idle time is flushed on context
- * switch. Softirqs in the end of hardirqs are also not a problem because
- * the idle time is flushed on hardirq time already.
- */
- vtime_account(tsk);
+ vtime_account_irq_enter(tsk);
irqtime_account_irq(tsk);
}

-static inline void vtime_account_irq_exit(struct task_struct *tsk)
+static inline void account_irq_exit_time(struct task_struct *tsk)
{
- /* On hard|softirq exit we always account to hard|softirq cputime */
- vtime_account_system(tsk);
+ vtime_account_irq_exit(tsk);
irqtime_account_irq(tsk);
}

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index bd461ad..bbb2c2c 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -15,6 +15,7 @@
*/

#include <linux/context_tracking.h>
+#include <linux/kvm_host.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/hardirq.h>
@@ -102,6 +103,24 @@ void user_exit(void)
local_irq_restore(flags);
}

+#ifdef CONFIG_KVM
+void guest_enter(void)
+{
+ if (vtime_accounting_enabled())
+ vtime_guest_enter(current);
+ else
+ __guest_enter();
+}
+
+void guest_exit(void)
+{
+ if (vtime_accounting_enabled())
+ vtime_guest_exit(current);
+ else
+ __guest_exit();
+}
+#endif
+

/**
* context_tracking_task_switch - context switch the syscall callbacks
diff --git a/kernel/fork.c b/kernel/fork.c
index 65ca6d2..e68a95b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1233,6 +1233,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
#ifndef CONFIG_VIRT_CPU_ACCOUNTING
p->prev_cputime.utime = p->prev_cputime.stime = 0;
#endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+ seqlock_init(&p->vtime_seqlock);
+ p->vtime_snap = 0;
+ p->vtime_snap_whence = VTIME_SLEEPING;
+#endif
+
#if defined(SPLIT_RSS_COUNTING)
memset(&p->rss_stat, 0, sizeof(p->rss_stat));
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 257002c..261022d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4666,6 +4666,7 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
*/
idle->sched_class = &idle_sched_class;
ftrace_graph_init_idle_task(idle, cpu);
+ vtime_init_idle(idle);
#if defined(CONFIG_SMP)
sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
#endif
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index a44ecdf..5500a81 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -492,7 +492,7 @@ void vtime_task_switch(struct task_struct *prev)
* vtime_account().
*/
#ifndef __ARCH_HAS_VTIME_ACCOUNT
-void vtime_account(struct task_struct *tsk)
+void vtime_account_irq_enter(struct task_struct *tsk)
{
if (!vtime_accounting_enabled())
return;
@@ -516,7 +516,7 @@ void vtime_account(struct task_struct *tsk)
}
vtime_account_system(tsk);
}
-EXPORT_SYMBOL_GPL(vtime_account);
+EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
#endif /* __ARCH_HAS_VTIME_ACCOUNT */

#else /* !CONFIG_VIRT_CPU_ACCOUNTING */
@@ -600,28 +600,55 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
#endif /* !CONFIG_VIRT_CPU_ACCOUNTING */

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-static DEFINE_PER_CPU(unsigned long long, cputime_snap);
+static unsigned long long vtime_delta(struct task_struct *tsk)
+{
+ unsigned long long clock;
+
+ clock = sched_clock();
+ if (clock < tsk->vtime_snap)
+ return 0;

-static cputime_t get_vtime_delta(void)
+ return clock - tsk->vtime_snap;
+}
+
+static cputime_t get_vtime_delta(struct task_struct *tsk)
{
- unsigned long long delta;
+ unsigned long long delta = vtime_delta(tsk);

- delta = sched_clock() - __this_cpu_read(cputime_snap);
- __this_cpu_add(cputime_snap, delta);
+ WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_SLEEPING);
+ tsk->vtime_snap += delta;

/* CHECKME: always safe to convert nsecs to cputime? */
return nsecs_to_cputime(delta);
}

+static void __vtime_account_system(struct task_struct *tsk)
+{
+ cputime_t delta_cpu = get_vtime_delta(tsk);
+
+ account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
+}
+
void vtime_account_system(struct task_struct *tsk)
{
- cputime_t delta_cpu;
+ if (!vtime_accounting_enabled())
+ return;
+
+ write_seqlock(&tsk->vtime_seqlock);
+ __vtime_account_system(tsk);
+ write_sequnlock(&tsk->vtime_seqlock);
+}

+void vtime_account_irq_exit(struct task_struct *tsk)
+{
if (!vtime_accounting_enabled())
return;

- delta_cpu = get_vtime_delta();
- account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
+ write_seqlock(&tsk->vtime_seqlock);
+ if (context_tracking_in_user())
+ tsk->vtime_snap_whence = VTIME_USER;
+ __vtime_account_system(tsk);
+ write_sequnlock(&tsk->vtime_seqlock);
}

void vtime_account_user(struct task_struct *tsk)
@@ -631,14 +658,46 @@ void vtime_account_user(struct task_struct *tsk)
if (!vtime_accounting_enabled())
return;

- delta_cpu = get_vtime_delta();
+ delta_cpu = get_vtime_delta(tsk);

+ write_seqlock(&tsk->vtime_seqlock);
+ tsk->vtime_snap_whence = VTIME_SYS;
account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
+ write_sequnlock(&tsk->vtime_seqlock);
}

+void vtime_user_enter(struct task_struct *tsk)
+{
+ if (!vtime_accounting_enabled())
+ return;
+
+ write_seqlock(&tsk->vtime_seqlock);
+ tsk->vtime_snap_whence = VTIME_USER;
+ __vtime_account_system(tsk);
+ write_sequnlock(&tsk->vtime_seqlock);
+}
+
+#ifdef CONFIG_KVM
+void vtime_guest_enter(struct task_struct *tsk)
+{
+ write_seqlock(&tsk->vtime_seqlock);
+ __vtime_account_system(tsk);
+ current->flags |= PF_VCPU;
+ write_sequnlock(&tsk->vtime_seqlock);
+}
+
+void vtime_guest_exit(struct task_struct *tsk)
+{
+ write_seqlock(&tsk->vtime_seqlock);
+ __vtime_account_system(tsk);
+ current->flags &= ~PF_VCPU;
+ write_sequnlock(&tsk->vtime_seqlock);
+}
+#endif
+
void vtime_account_idle(struct task_struct *tsk)
{
- cputime_t delta_cpu = get_vtime_delta();
+ cputime_t delta_cpu = get_vtime_delta(tsk);

account_idle_time(delta_cpu);
}
@@ -647,4 +706,116 @@ bool vtime_accounting_enabled(void)
{
return context_tracking_active();
}
+
+void arch_vtime_task_switch(struct task_struct *prev)
+{
+ write_seqlock(&prev->vtime_seqlock);
+ prev->vtime_snap_whence = VTIME_SLEEPING;
+ write_sequnlock(&prev->vtime_seqlock);
+
+ write_seqlock(&current->vtime_seqlock);
+ current->vtime_snap_whence = VTIME_SYS;
+ current->vtime_snap = sched_clock();
+ write_sequnlock(&current->vtime_seqlock);
+}
+
+void vtime_init_idle(struct task_struct *t)
+{
+ unsigned long flags;
+
+ write_seqlock_irqsave(&t->vtime_seqlock, flags);
+ t->vtime_snap_whence = VTIME_SYS;
+ t->vtime_snap = sched_clock();
+ write_sequnlock_irqrestore(&t->vtime_seqlock, flags);
+}
+
+cputime_t task_gtime(struct task_struct *t)
+{
+ unsigned long flags;
+ unsigned int seq;
+ cputime_t gtime;
+
+ do {
+ seq = read_seqbegin_irqsave(&t->vtime_seqlock, flags);
+
+ gtime = t->gtime;
+ if (t->flags & PF_VCPU)
+ gtime += vtime_delta(t);
+
+ } while (read_seqretry_irqrestore(&t->vtime_seqlock, seq, flags));
+
+ return gtime;
+}
+
+/*
+ * Fetch cputime raw values from fields of task_struct and
+ * add up the pending nohz execution time since the last
+ * cputime snapshot.
+ */
+static void
+fetch_task_cputime(struct task_struct *t,
+ cputime_t *u_dst, cputime_t *s_dst,
+ cputime_t *u_src, cputime_t *s_src,
+ cputime_t *udelta, cputime_t *sdelta)
+{
+ unsigned long flags;
+ unsigned int seq;
+ unsigned long long delta;
+
+ do {
+ *udelta = 0;
+ *sdelta = 0;
+
+ seq = read_seqbegin_irqsave(&t->vtime_seqlock, flags);
+
+ if (u_dst)
+ *u_dst = *u_src;
+ if (s_dst)
+ *s_dst = *s_src;
+
+ /* Task is sleeping, nothing to add */
+ if (t->vtime_snap_whence == VTIME_SLEEPING ||
+ is_idle_task(t))
+ continue;
+
+ delta = vtime_delta(t);
+
+ /*
+ * Task runs either in user or kernel space, add pending nohz time to
+ * the right place.
+ */
+ if (t->vtime_snap_whence == VTIME_USER || t->flags & PF_VCPU) {
+ *udelta = delta;
+ } else {
+ if (t->vtime_snap_whence == VTIME_SYS)
+ *sdelta = delta;
+ }
+ } while (read_seqretry_irqrestore(&t->vtime_seqlock, seq, flags));
+}
+
+
+void task_cputime(struct task_struct *t, cputime_t *utime, cputime_t *stime)
+{
+ cputime_t udelta, sdelta;
+
+ fetch_task_cputime(t, utime, stime, &t->utime,
+ &t->stime, &udelta, &sdelta);
+ if (utime)
+ *utime += udelta;
+ if (stime)
+ *stime += sdelta;
+}
+
+void task_cputime_scaled(struct task_struct *t,
+ cputime_t *utimescaled, cputime_t *stimescaled)
+{
+ cputime_t udelta, sdelta;
+
+ fetch_task_cputime(t, utimescaled, stimescaled,
+ &t->utimescaled, &t->stimescaled, &udelta, &sdelta);
+ if (utimescaled)
+ *utimescaled += cputime_to_scaled(udelta);
+ if (stimescaled)
+ *stimescaled += cputime_to_scaled(sdelta);
+}
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
diff --git a/kernel/softirq.c b/kernel/softirq.c
index ed567ba..f5cc25f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -221,7 +221,7 @@ asmlinkage void __do_softirq(void)
current->flags &= ~PF_MEMALLOC;

pending = local_softirq_pending();
- vtime_account_irq_enter(current);
+ account_irq_enter_time(current);

__local_bh_disable((unsigned long)__builtin_return_address(0),
SOFTIRQ_OFFSET);
@@ -272,7 +272,7 @@ restart:

lockdep_softirq_exit();

- vtime_account_irq_exit(current);
+ account_irq_exit_time(current);
__local_bh_enable(SOFTIRQ_OFFSET);
tsk_restore_flags(current, old_flags, PF_MEMALLOC);
}
@@ -341,7 +341,7 @@ static inline void invoke_softirq(void)
*/
void irq_exit(void)
{
- vtime_account_irq_exit(current);
+ account_irq_exit_time(current);
trace_hardirq_exit();
sub_preempt_count(IRQ_EXIT_OFFSET);
if (!in_interrupt() && local_softirq_pending())
--
1.7.5.4

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