linux-kernel - [tip: timers/core] timekeeping: Rework timekeeping_inject_offset() to use shadow

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Message-ID: <172987927903.1442.6753504312627902580.tip-bot2@tip-bot2>
Date: Fri, 25 Oct 2024 18:01:19 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 Thomas Gleixner <tglx@...utronix.de>, John Stultz <jstultz@...gle.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timekeeping: Rework timekeeping_inject_offset() to
 use shadow_timekeeper

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     82214756d35f48056fe36aa4d95a22e44a3b2619
Gitweb:        https://git.kernel.org/tip/82214756d35f48056fe36aa4d95a22e44a3b2619
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Wed, 09 Oct 2024 10:29:10 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 25 Oct 2024 19:49:15 +02:00

timekeeping: Rework timekeeping_inject_offset() to use shadow_timekeeper

Updates of the timekeeper can be done by operating on the shadow timekeeper
and afterwards copying the result into the real timekeeper. This has the
advantage, that the sequence count write protected region is kept as small
as possible.

Convert timekeeping_inject_offset() to use this scheme.

That allows to use a scoped_guard() for locking the timekeeper lock as the
usage of the shadow timekeeper allows a rollback in the error case instead
of the full timekeeper update of the original code.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: John Stultz <jstultz@...gle.com>
Link: https://lore.kernel.org/all/20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-17-554456a44a15@linutronix.de

---
 kernel/time/timekeeping.c | 41 ++++++++++++++------------------------
 1 file changed, 16 insertions(+), 25 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 1b8db11..7e865f0 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1550,40 +1550,31 @@ EXPORT_SYMBOL(do_settimeofday64);
  */
 static int timekeeping_inject_offset(const struct timespec64 *ts)
 {
-	struct timekeeper *tk = &tk_core.timekeeper;
-	unsigned long flags;
-	struct timespec64 tmp;
-	int ret = 0;
-
 	if (ts->tv_nsec < 0 || ts->tv_nsec >= NSEC_PER_SEC)
 		return -EINVAL;
 
-	raw_spin_lock_irqsave(&tk_core.lock, flags);
-	write_seqcount_begin(&tk_core.seq);
-
-	timekeeping_forward_now(tk);
-
-	/* Make sure the proposed value is valid */
-	tmp = timespec64_add(tk_xtime(tk), *ts);
-	if (timespec64_compare(&tk->wall_to_monotonic, ts) > 0 ||
-	    !timespec64_valid_settod(&tmp)) {
-		ret = -EINVAL;
-		goto error;
-	}
+	scoped_guard (raw_spinlock_irqsave, &tk_core.lock) {
+		struct timekeeper *tks = &tk_core.shadow_timekeeper;
+		struct timespec64 tmp;
 
-	tk_xtime_add(tk, ts);
-	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *ts));
+		timekeeping_forward_now(tks);
 
-error: /* even if we error out, we forwarded the time, so call update */
-	timekeeping_update(&tk_core, tk, TK_UPDATE_ALL | TK_MIRROR);
+		/* Make sure the proposed value is valid */
+		tmp = timespec64_add(tk_xtime(tks), *ts);
+		if (timespec64_compare(&tks->wall_to_monotonic, ts) > 0 ||
+		    !timespec64_valid_settod(&tmp)) {
+			timekeeping_restore_shadow(&tk_core);
+			return -EINVAL;
+		}
 
-	write_seqcount_end(&tk_core.seq);
-	raw_spin_unlock_irqrestore(&tk_core.lock, flags);
+		tk_xtime_add(tks, ts);
+		tk_set_wall_to_mono(tks, timespec64_sub(tks->wall_to_monotonic, *ts));
+		timekeeping_update_from_shadow(&tk_core, TK_UPDATE_ALL);
+	}
 
 	/* Signal hrtimers about time change */
 	clock_was_set(CLOCK_SET_WALL);
-
-	return ret;
+	return 0;
 }
 
 /*