[PATCH net v3 4/5] ptp: vclock: serialize extended samples with counter updates
flat view
WARM2d
SUPERSEDED
From: James Hilliard <hidden>
Date: 2026-10-13 19:19:53
Also in:
lkml
Subsystem:
networking drivers, ptp hardware clock support, ptp virtual clock support, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Richard Cochran, Yangbo Lu, Linus Torvalds
Revision v3 of 2 in this series.
Revisions (2)
- v3 current
- v4 [diff vs current]
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 <redacted>
---
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 eea207e5a889..6675466bc307 100644
--- a/drivers/ptp/ptp_vclock.c
+++ b/drivers/ptp/ptp_vclock.c@@ -113,20 +113,18 @@ 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)); - mutex_unlock(&vclock->lock); + 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); + *ts = ns_to_timespec64(ns); + } + mutex_unlock(&vclock->lock); - return 0; + return err; } static int ptp_vclock_settime(struct ptp_clock_info *ptp,
@@ -152,20 +150,18 @@ 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)); - mutex_unlock(&vclock->lock); + 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); + xtstamp->device = ns_to_ktime(ns); + } + mutex_unlock(&vclock->lock); - return 0; + return err; } static long ptp_vclock_refresh(struct ptp_clock_info *ptp)
--
2.53.0