[tip: timers/core] posix-cpu-timers: Provide quick sample function for itimer

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     19298fbf453c90a6cf72288155f80c6f55e9139d
Gitweb:        https://git.kernel.org/tip/19298fbf453c90a6cf72288155f80c6f55e9139d
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Wed, 21 Aug 2019 21:08:51 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 28 Aug 2019 11:50:26 +02:00

posix-cpu-timers: Provide quick sample function for itimer

get_itimer() needs a sample of the current thread group cputime. It invokes
thread_group_cputimer() - which is a misnomer. That function also starts
eventually the group cputime accouting which is bogus because the
accounting is already active when a timer is armed.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190821192919.599658199@xxxxxxxxxxxxx

---
 include/linux/sched/cputime.h  |  2 +-
 kernel/time/posix-cpu-timers.c | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/cputime.h b/include/linux/sched/cputime.h
index 53f883f..6de7b38 100644
--- a/include/linux/sched/cputime.h
+++ b/include/linux/sched/cputime.h
@@ -62,7 +62,7 @@ extern void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
  */
 void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times);
 void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);
-
+void thread_group_sample_cputime(struct task_struct *tsk, struct task_cputime *times);
 
 /*
  * The following are functions that support scheduler-internal time accounting.
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 4426a0f..c22b6b6 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -232,6 +232,27 @@ static inline void sample_cputime_atomic(struct task_cputime *times,
 	times->sum_exec_runtime = atomic64_read(&atomic_times->sum_exec_runtime);
 }
 
+/**
+ * thread_group_sample_cputime - Sample cputime for a given task
+ * @tsk:	Task for which cputime needs to be started
+ * @iimes:	Storage for time samples
+ *
+ * Called from sys_getitimer() to calculate the expiry time of an active
+ * timer. That means group cputime accounting is already active. Called
+ * with task sighand lock held.
+ *
+ * Updates @times with an uptodate sample of the thread group cputimes.
+ */
+void thread_group_sample_cputime(struct task_struct *tsk,
+				struct task_cputime *times)
+{
+	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+
+	WARN_ON_ONCE(!cputimer->running);
+
+	sample_cputime_atomic(times, &cputimer->cputime_atomic);
+}
+
 void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
 {
 	struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;