posix-cpu-timers: Sample directly in timer check

The thread group accounting is active, otherwise the expiry function would
not be running. Sample the thread group time directly.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192919.780348088@linutronix.de

kernel/time/posix-cpu-timers.c

@@ -921,9 +921,10 @@ static void check_process_timers(struct task_struct *tsk,
 	sig->cputimer.checking_timer = true;
 
 	/*
-	 * Collect the current process totals.
+	 * Collect the current process totals. Group accounting is active
+	 * so the sample can be taken directly.
 	 */
-	thread_group_cputimer(tsk, &cputime);
+	sample_cputime_atomic(&cputime, &sig->cputimer.cputime_atomic);
 	utime = cputime.utime;
 	ptime = utime + cputime.stime;
 	sum_sched_runtime = cputime.sum_exec_runtime;