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Date:	Sat, 29 Dec 2012 17:42:44 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 05/27] cputime: Safely read cputime of full dynticks CPUs

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.

FIXME: do the same for idle and guest time.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Alessio Igor Bogani <abogani@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Chris Metcalf <cmetcalf@...era.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Geoff Levand <geoff@...radead.org>
Cc: Gilad Ben Yossef <gilad@...yossef.com>
Cc: Hakan Akkan <hakanakkan@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 arch/s390/kernel/vtime.c      |    6 +-
 include/asm-generic/cputime.h |    1 +
 include/linux/hardirq.h       |    4 +-
 include/linux/init_task.h     |   11 ++++
 include/linux/sched.h         |   16 +++++
 include/linux/vtime.h         |   40 +++++++-------
 kernel/context_tracking.c     |    2 +-
 kernel/fork.c                 |    6 ++
 kernel/sched/cputime.c        |  123 ++++++++++++++++++++++++++++++-----------
 kernel/softirq.c              |    6 +-
 10 files changed, 154 insertions(+), 61 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/asm-generic/cputime.h b/include/asm-generic/cputime.h
index 9a62937..3e704d5 100644
--- a/include/asm-generic/cputime.h
+++ b/include/asm-generic/cputime.h
@@ -10,6 +10,7 @@ typedef unsigned long __nocast cputime_t;
 #define cputime_to_jiffies(__ct)	(__force unsigned long)(__ct)
 #define cputime_to_scaled(__ct)		(__ct)
 #define jiffies_to_cputime(__hz)	(__force cputime_t)(__hz)
+#define jiffies_to_scaled(__hz)		(__force cputime_t)(__hz)
 
 typedef u64 __nocast cputime64_t;
 
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..a6ef59f 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),	\
+	.prev_jiffies = INITIAL_JIFFIES, /* CHECKME */		\
+	.prev_jiffies_whence = JIFFIES_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/sched.h b/include/linux/sched.h
index d57e20f..3bca36e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1368,6 +1368,15 @@ struct task_struct {
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 	struct cputime prev_cputime;
 #endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+	seqlock_t vtime_seqlock;
+	long prev_jiffies;
+	enum {
+		JIFFIES_SLEEPING = 0,
+		JIFFIES_USER,
+		JIFFIES_SYS,
+	} prev_jiffies_whence;
+#endif
 	unsigned long nvcsw, nivcsw; /* context switch counts */
 	struct timespec start_time; 		/* monotonic time */
 	struct timespec real_start_time;	/* boot based time */
@@ -1792,6 +1801,12 @@ static inline void put_task_struct(struct task_struct *t)
 		__put_task_struct(t);
 }
 
+#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);
+#else
 static inline void task_cputime(struct task_struct *t,
 				cputime_t *utime, cputime_t *stime)
 {
@@ -1810,6 +1825,7 @@ static inline void task_cputime_scaled(struct task_struct *t,
 	if (stimescaled)
 		*stimescaled = t->stimescaled;
 }
+#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 e57020d..81c7d84 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -9,52 +9,52 @@ extern void vtime_account_system(struct task_struct *tsk);
 extern void vtime_account_system_irqsafe(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(void);
-#else
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 static inline bool vtime_accounting(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_system_irqsafe(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(void) { return false; }
 #endif
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-static inline void arch_vtime_task_switch(struct task_struct *tsk) { }
+extern void arch_vtime_task_switch(struct task_struct *tsk);
+extern void vtime_account_irq_exit(struct task_struct *tsk);
+extern void vtime_user_enter(struct task_struct *tsk);
+extern bool vtime_accounting(void);
+#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_enter_user(struct task_struct *tsk) { }
 #endif
 
+
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 extern void irqtime_account_irq(struct task_struct *tsk);
 #else
 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 ca1e073..bd2f2fc 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -56,7 +56,7 @@ void user_enter(void)
 	local_irq_save(flags);
 	if (__this_cpu_read(context_tracking.active) &&
 	    __this_cpu_read(context_tracking.state) != IN_USER) {
-		vtime_account_system(current);
+		vtime_user_enter(current);
 		/*
 		 * At this stage, only low level arch entry code remains and
 		 * then we'll run in userspace. We can assume there won't be
diff --git a/kernel/fork.c b/kernel/fork.c
index 8e934d2..62892a5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1225,6 +1225,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 	p->prev_cputime.utime = p->prev_cputime.stime = 0;
 #endif
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+	seqlock_init(&p->vtime_seqlock);
+	p->prev_jiffies_whence = JIFFIES_SLEEPING; /*CHECKME: idle tasks? */
+	p->prev_jiffies = jiffies;
+#endif
+
 #if defined(SPLIT_RSS_COUNTING)
 	memset(&p->rss_stat, 0, sizeof(p->rss_stat));
 #endif
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 0603671..bad19b2 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -484,7 +484,7 @@ 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 (!in_interrupt()) {
 		/*
@@ -505,7 +505,7 @@ 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 */
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING */
 
@@ -616,41 +616,67 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
 #endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-static DEFINE_PER_CPU(long, last_jiffies) = INITIAL_JIFFIES;
-
-static cputime_t get_vtime_delta(void)
+static cputime_t get_vtime_delta(struct task_struct *tsk)
 {
 	long delta;
 
-	delta = jiffies - __this_cpu_read(last_jiffies);
-	__this_cpu_add(last_jiffies, delta);
+	delta = jiffies - tsk->prev_jiffies;
+	tsk->prev_jiffies += delta;
 
 	return jiffies_to_cputime(delta);
 }
 
-void vtime_account_system(struct task_struct *tsk)
+static void __vtime_account_system(struct task_struct *tsk)
 {
-	cputime_t delta_cpu = get_vtime_delta();
+	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)
+{
+	write_seqlock(&tsk->vtime_seqlock);
+	__vtime_account_system(tsk);
+	write_sequnlock(&tsk->vtime_seqlock);
+}
+
+void vtime_account_irq_exit(struct task_struct *tsk)
+{
+	write_seqlock(&tsk->vtime_seqlock);
+	if (context_tracking_in_user())
+		tsk->prev_jiffies_whence = JIFFIES_USER;
+	__vtime_account_system(tsk);
+	write_sequnlock(&tsk->vtime_seqlock);
+}
+
 void vtime_account_user(struct task_struct *tsk)
 {
-	cputime_t delta_cpu = get_vtime_delta();
+	cputime_t delta_cpu = get_vtime_delta(tsk);
 
 	/*
 	 * This is an unfortunate hack: if we flush user time only on
 	 * irq entry, we miss the jiffies update and the time is spuriously
 	 * accounted to system time.
 	 */
-	if (context_tracking_in_user())
+	if (context_tracking_in_user()) {
+		write_seqlock(&tsk->vtime_seqlock);
+		tsk->prev_jiffies_whence = JIFFIES_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)
+{
+	write_seqlock(&tsk->vtime_seqlock);
+	tsk->prev_jiffies_whence = JIFFIES_USER;
+	__vtime_account_system(tsk);
+	write_sequnlock(&tsk->vtime_seqlock);
 }
 
 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);
 }
@@ -660,31 +686,64 @@ bool vtime_accounting(void)
 	return context_tracking_active();
 }
 
-static int __cpuinit vtime_cpu_notify(struct notifier_block *self,
-				      unsigned long action, void *hcpu)
+void arch_vtime_task_switch(struct task_struct *prev)
 {
-	long cpu = (long)hcpu;
-	long *last_jiffies_cpu = per_cpu_ptr(&last_jiffies, cpu);
+	write_seqlock(&prev->vtime_seqlock);
+	prev->prev_jiffies_whence = JIFFIES_SLEEPING;
+	write_sequnlock(&prev->vtime_seqlock);
 
-	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
-		/*
-		 * CHECKME: ensure that's visible by the CPU
-		 * once it wakes up
-		 */
-		*last_jiffies_cpu = jiffies;
-	default:
-		break;
-	}
+	write_seqlock(&current->vtime_seqlock);
+	current->prev_jiffies_whence = JIFFIES_SYS;
+	current->prev_jiffies = jiffies;
+	write_sequnlock(&current->vtime_seqlock);
+}
+
+void task_cputime(struct task_struct *t, cputime_t *utime, cputime_t *stime)
+{
+	unsigned int seq;
+	long delta;
+
+	do {
+		seq = read_seqbegin(&t->vtime_seqlock);
+
+		*utime = t->utime;
+		*stime = t->stime;
+
+		if (t->prev_jiffies_whence == JIFFIES_SLEEPING || 
+		    is_idle_task(t))
+			continue;
 
-	return NOTIFY_OK;
+		delta = jiffies - t->prev_jiffies;
+
+		if (t->prev_jiffies_whence == JIFFIES_USER)
+			*utime += delta;
+		else if (t->prev_jiffies_whence == JIFFIES_SYS)
+			*stime += delta;
+	} while (read_seqretry(&t->vtime_seqlock, seq));
 }
 
-static int __init init_vtime(void)
+void task_cputime_scaled(struct task_struct *t,
+			 cputime_t *utimescaled, cputime_t *stimescaled)
 {
-	cpu_notifier(vtime_cpu_notify, 0);
-	return 0;
+	unsigned int seq;
+	long delta;
+
+	do {
+		seq = read_seqbegin(&t->vtime_seqlock);
+
+		*utimescaled = t->utimescaled;
+		*stimescaled = t->stimescaled;
+
+		if (t->prev_jiffies_whence == JIFFIES_SLEEPING || 
+		    is_idle_task(t))
+			continue;
+
+		delta = jiffies - t->prev_jiffies;
+
+		if (t->prev_jiffies_whence == JIFFIES_USER)
+			*utimescaled += jiffies_to_scaled(delta);
+		else if (t->prev_jiffies_whence == JIFFIES_SYS)
+			*stimescaled += jiffies_to_scaled(delta);
+	} while (read_seqretry(&t->vtime_seqlock, seq));
 }
-early_initcall(init_vtime);
 #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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