linux-kernel - [PATCH 08/14] vdso/gettimeofday: Introduce vdso_set

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Message-Id: <20250701-vdso-auxclock-v1-8-df7d9f87b9b8@linutronix.de>
Date: Tue, 01 Jul 2025 10:58:02 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
 Vincenzo Frascino <vincenzo.frascino@....com>, 
 Shuah Khan <shuah@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, John Stultz <jstultz@...gle.com>, 
 Stephen Boyd <sboyd@...nel.org>, Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org, 
 Richard Cochran <richardcochran@...il.com>, 
 Christopher Hall <christopher.s.hall@...el.com>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Miroslav Lichvar <mlichvar@...hat.com>, 
 Werner Abt <werner.abt@...nberg-usa.com>, 
 David Woodhouse <dwmw2@...radead.org>, Stephen Boyd <sboyd@...nel.org>, 
 Kurt Kanzenbach <kurt@...utronix.de>, Nam Cao <namcao@...utronix.de>, 
 Antoine Tenart <atenart@...nel.org>, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH 08/14] 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@...utronix.de>
---
 lib/vdso/gettimeofday.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index 215151bd5a1320ee6edda8f334d47c739577f696..50611ba28abfcfc7841616e8787101ea1ffcb7d8 100644
--- a/lib/vdso/gettimeofday.c
+++ b/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

-- 
2.50.0