linux-kernel - [patch V2 04/38] posix-cpu-timers: Provide quick sample function for itimer

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Date:   Wed, 21 Aug 2019 21:08:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Christoph Hellwig <hch@....de>
Subject: [patch V2 04/38] 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@...utronix.de>
---
 include/linux/sched/cputime.h  |    2 +-
 kernel/time/posix-cpu-timers.c |   21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

--- a/include/linux/sched/cputime.h
+++ b/include/linux/sched/cputime.h
@@ -62,7 +62,7 @@ extern void cputime_adjust(struct task_c
  */
 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.
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -232,6 +232,27 @@ static inline void sample_cputime_atomic
 	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;