linux-kernel - [patch 5/8] time/timekeeping: Avoid invoking clock_was

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Date:   Tue, 27 Apr 2021 10:25:42 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Peter Xu <peterx@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        John Stultz <john.stultz@...aro.org>
Subject: [patch 5/8] time/timekeeping: Avoid invoking clock_was_set() twice

do_adjtimex() might end up scheduling a delayed clock_was_set() via
timekeeping_advance() and then invoke clock_was_set() directly which is
pointless.

Make timekeeping_advance() return whether an invocation of clock_was_set()
is required and handle it at the call sites which allows do_adjtimex() to
issue a single direct call if required.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/timekeeping.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2126,7 +2126,7 @@ static u64 logarithmic_accumulation(stru
  * timekeeping_advance - Updates the timekeeper to the current time and
  * current NTP tick length
  */
-static void timekeeping_advance(enum timekeeping_adv_mode mode)
+static bool timekeeping_advance(enum timekeeping_adv_mode mode)
 {
 	struct timekeeper *real_tk = &tk_core.timekeeper;
 	struct timekeeper *tk = &shadow_timekeeper;
@@ -2197,9 +2197,8 @@ static void timekeeping_advance(enum tim
 	write_seqcount_end(&tk_core.seq);
 out:
 	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
-	if (clock_set)
-		/* Have to call _delayed version, since in irq context*/
-		clock_was_set_delayed();
+
+	return !!clock_set;
 }
 
 /**
@@ -2208,7 +2207,8 @@ static void timekeeping_advance(enum tim
  */
 void update_wall_time(void)
 {
-	timekeeping_advance(TK_ADV_TICK);
+	if (timekeeping_advance(TK_ADV_TICK))
+		clock_was_set_delayed();
 }
 
 /**
@@ -2388,8 +2388,9 @@ int do_adjtimex(struct __kernel_timex *t
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
 	struct audit_ntp_data ad;
-	unsigned long flags;
+	bool clock_set = false;
 	struct timespec64 ts;
+	unsigned long flags;
 	s32 orig_tai, tai;
 	int ret;
 
@@ -2424,6 +2425,7 @@ int do_adjtimex(struct __kernel_timex *t
 	if (tai != orig_tai) {
 		__timekeeping_set_tai_offset(tk, tai);
 		timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
+		clock_set = true;
 	}
 	tk_update_leap_state(tk);
 
@@ -2434,9 +2436,9 @@ int do_adjtimex(struct __kernel_timex *t
 
 	/* Update the multiplier immediately if frequency was set directly */
 	if (txc->modes & (ADJ_FREQUENCY | ADJ_TICK))
-		timekeeping_advance(TK_ADV_FREQ);
+		clock_set |= timekeeping_advance(TK_ADV_FREQ);
 
-	if (tai != orig_tai)
+	if (clock_set)
 		clock_was_set();
 
 	ntp_notify_cmos_timer();