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pps: Simplify capture and event processing

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Use local variables for the captured timehand and timecounter in pps_event().
This fixes a potential issue in the nsec preparation for hardpps().  Here the
timecounter was accessed through the captured timehand after the generation was
checked.

Make a snapshot of the relevent timehand values early in pps_event().  Check
the timehand generation only once during the capture and event processing.  Use
atomic_thread_fence_acq() similar to the other readers.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/604
This commit is contained in:
Sebastian Huber 2023-02-27 14:49:09 -07:00 committed by Warner Losh
parent cb2a028b15
commit fd88f4e190
1 changed files with 20 additions and 18 deletions
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38
sys/kern/kern_tc.c
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@ -1772,14 +1772,14 @@ pps_capture(struct pps_state *pps)
#endif
tc = th->th_counter;
pps->capcount = tc->tc_get_timecount(tc);
atomic_thread_fence_acq();
if (pps->capgen != th->th_generation)
pps->capgen = 0;
}
void
pps_event(struct pps_state *pps, int event)
{
struct timehands *capth;
struct timecounter *captc;
uint64_t capth_scale;
struct bintime bt;
struct timespec ts, *tsp, *osp;
u_int tcount, *pcount;
@ -1798,9 +1798,17 @@ pps_event(struct pps_state *pps, int event)
/* Nothing to do if not currently set to capture this event type. */
if ((event & pps->ppsparam.mode) == 0)
return;
/* Make a snapshot of the captured timehand */
capth = pps->capth;
captc = capth->th_counter;
capth_scale = capth->th_scale;
tcount = capth->th_offset_count;
bt = capth->th_bintime;
/* If the timecounter was wound up underneath us, bail out. */
if (pps->capgen == 0 || pps->capgen !=
atomic_load_acq_int(&pps->capth->th_generation))
atomic_thread_fence_acq();
if (pps->capgen == 0 || pps->capgen != capth->th_generation)
return;
/* Things would be easier with arrays. */
@ -1838,25 +1846,19 @@ pps_event(struct pps_state *pps, int event)
* If the timecounter changed, we cannot compare the count values, so
* we have to drop the rest of the PPS-stuff until the next event.
*/
if (pps->ppstc != pps->capth->th_counter) {
pps->ppstc = pps->capth->th_counter;
if (__predict_false(pps->ppstc != captc)) {
pps->ppstc = captc;
*pcount = pps->capcount;
pps->ppscount[2] = pps->capcount;
return;
}
/* Convert the count to a timespec. */
tcount = pps->capcount - pps->capth->th_offset_count;
tcount &= pps->capth->th_counter->tc_counter_mask;
bt = pps->capth->th_bintime;
bintime_addx(&bt, pps->capth->th_scale * tcount);
tcount = pps->capcount - tcount;
tcount &= captc->tc_counter_mask;
bintime_addx(&bt, capth_scale * tcount);
bintime2timespec(&bt, &ts);
/* If the timecounter was wound up underneath us, bail out. */
atomic_thread_fence_acq();
if (pps->capgen != pps->capth->th_generation)
return;
*pcount = pps->capcount;
(*pseq)++;
*tsp = ts;
@ -1890,9 +1892,9 @@ pps_event(struct pps_state *pps, int event)
*/
tcount = pps->capcount - pps->ppscount[2];
pps->ppscount[2] = pps->capcount;
tcount &= pps->capth->th_counter->tc_counter_mask;
tcount &= captc->tc_counter_mask;
scale = (uint64_t)1 << 63;
scale /= pps->capth->th_counter->tc_frequency;
scale /= captc->tc_frequency;
scale *= 2;
bt.sec = 0;
bt.frac = 0;