vdso/gettimeofday: Introduce vdso_set_timespec()

This code is duplicated and with the introduction of auxiliary clocks will
be duplicated even more.

Introduce a helper.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250701-vdso-auxclock-v1-8-df7d9f87b9b8@linutronix.de

Author: t-8ch

lib/vdso/gettimeofday.c

@@ -77,6 +77,16 @@ static __always_inline bool vdso_clockid_valid(clockid_t clock)
 	return likely((u32) clock < MAX_CLOCKS);
 }
 
+/*
+ * Must not be invoked within the sequence read section as a race inside
+ * that loop could result in __iter_div_u64_rem() being extremely slow.
+ */
+static __always_inline void vdso_set_timespec(struct __kernel_timespec *ts, u64 sec, u64 ns)
+{
+	ts->tv_sec = sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+	ts->tv_nsec = ns;
+}
+
 #ifdef CONFIG_TIME_NS
 
 #ifdef CONFIG_GENERIC_VDSO_DATA_STORE
@@ -122,12 +132,7 @@ bool do_hres_timens(const struct vdso_time_data *vdns, const struct vdso_clock *
 	sec += offs->sec;
 	ns += offs->nsec;
 
-	/*
-	 * Do this outside the loop: a race inside the loop could result
-	 * in __iter_div_u64_rem() being extremely slow.
-	 */
-	ts->tv_sec = sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
-	ts->tv_nsec = ns;
+	vdso_set_timespec(ts, sec, ns);
 
 	return true;
 }
@@ -188,12 +193,7 @@ bool do_hres(const struct vdso_time_data *vd, const struct vdso_clock *vc,
 		sec = vdso_ts->sec;
 	} while (unlikely(vdso_read_retry(vc, seq)));
 
-	/*
-	 * Do this outside the loop: a race inside the loop could result
-	 * in __iter_div_u64_rem() being extremely slow.
-	 */
-	ts->tv_sec = sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
-	ts->tv_nsec = ns;
+	vdso_set_timespec(ts, sec, ns);
 
 	return true;
 }
@@ -223,12 +223,8 @@ bool do_coarse_timens(const struct vdso_time_data *vdns, const struct vdso_clock
 	sec += offs->sec;
 	nsec += offs->nsec;
 
-	/*
-	 * Do this outside the loop: a race inside the loop could result
-	 * in __iter_div_u64_rem() being extremely slow.
-	 */
-	ts->tv_sec = sec + __iter_div_u64_rem(nsec, NSEC_PER_SEC, &nsec);
-	ts->tv_nsec = nsec;
+	vdso_set_timespec(ts, sec, nsec);
+
 	return true;
 }
 #else