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ptp: vclock: serialize extended samples with counter updates

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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: f0067ebfc4 ("ptp: add gettimex64() to virtual clocks.")
Fixes: 21fad63084 ("ptp: add getcrosststamp() to virtual clocks.")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Link: https://patch.msgid.link/20261026-ptp-vclock-sampling-v6-4-e705612541f1@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
James Hilliard 2026-10-26 12:11:30 -06:00 committed by Jakub Kicinski
parent d1bdfdafd6
commit d3fcce5afe
1 changed files with 14 additions and 18 deletions
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32
drivers/ptp/ptp_vclock.c
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@ -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)