From d3fcce5afe3bb62e8f7a2efb29e43da4fe4ae1f3 Mon Sep 17 00:00:00 2001 From: James Hilliard Date: Mon, 26 Oct 2026 12:11:30 -0600 Subject: [PATCH] ptp: vclock: serialize extended samples with counter updates The extended and cross-timestamp callbacks sample the physical clock before taking the virtual clock mutex. A concurrent frequency adjustment can advance the timecounter and change its multiplier in between, so the older sample is converted using a different frequency than the one in effect when it was taken. Take the mutex before sampling and keep it held through the conversion. Retain timecounter_cyc2time() and its existing conversion window. A PHC sample need not advance the counter: for example, e1000e explicitly allows non-monotonic SYSTIM readings. Treating a slightly older sample as a forward delta would instead advance virtual time by nearly a full counter wrap. This race was found by code inspection of the virtual clock sampling paths. Fixes: f0067ebfc42b ("ptp: add gettimex64() to virtual clocks.") Fixes: 21fad63084c2 ("ptp: add getcrosststamp() to virtual clocks.") Signed-off-by: James Hilliard Link: https://patch.msgid.link/20261026-ptp-vclock-sampling-v6-4-e705612541f1@gmail.com Signed-off-by: Jakub Kicinski --- drivers/ptp/ptp_vclock.c | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-) diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c index b97f3a877260..679ae40916f7 100644 --- a/drivers/ptp/ptp_vclock.c +++ b/drivers/ptp/ptp_vclock.c @@ -115,20 +115,18 @@ static int ptp_vclock_gettimex(struct ptp_clock_info *ptp, struct ptp_clock *pptp = vclock->pclock; struct timespec64 pts; int err; - u64 ns; - - err = pptp->info->getcyclesx64(pptp->info, &pts, sts); - if (err) - return err; if (mutex_lock_interruptible(&vclock->lock)) return -EINTR; - ns = timecounter_cyc2time(&vclock->tc, timespec64_to_ns(&pts)); + err = pptp->info->getcyclesx64(pptp->info, &pts, sts); + if (!err) { + u64 ns = timecounter_cyc2time(&vclock->tc, timespec64_to_ns(&pts)); + + *ts = ns_to_timespec64(ns); + } mutex_unlock(&vclock->lock); - *ts = ns_to_timespec64(ns); - - return 0; + return err; } static int ptp_vclock_settime(struct ptp_clock_info *ptp, @@ -154,20 +152,18 @@ static int ptp_vclock_getcrosststamp(struct ptp_clock_info *ptp, struct ptp_vclock *vclock = info_to_vclock(ptp); struct ptp_clock *pptp = vclock->pclock; int err; - u64 ns; - - err = pptp->info->getcrosscycles(pptp->info, xtstamp); - if (err) - return err; if (mutex_lock_interruptible(&vclock->lock)) return -EINTR; - ns = timecounter_cyc2time(&vclock->tc, ktime_to_ns(xtstamp->device)); + err = pptp->info->getcrosscycles(pptp->info, xtstamp); + if (!err) { + u64 ns = timecounter_cyc2time(&vclock->tc, ktime_to_ns(xtstamp->device)); + + xtstamp->device = ns_to_ktime(ns); + } mutex_unlock(&vclock->lock); - xtstamp->device = ns_to_ktime(ns); - - return 0; + return err; } static long ptp_vclock_refresh(struct ptp_clock_info *ptp)