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.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
[fixed kvm module related build errors]
Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>

1 files changed, 181 insertions, 12 deletions

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index a44ecdf809a1..082e05d915b4 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 +658,44 @@ 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);
+}
+
+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);
 }
 
 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 +704,116 @@ 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 */