svn commit: r326973 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Tue Dec 19 10:05:45 2017
New Revision: 326973
URL: https://svnweb.freebsd.org/changeset/base/326973

Log:
  Use atomic_load(9) to read ppsinfo sequence numbers.
  
  In this case volatile qualifiers enusre that a compiler does not
  optimize the accesses out.
  
  Reviewed by:	alc, jhb
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D13534

Modified:
  head/sys/kern/kern_tc.c

Modified: head/sys/kern/kern_tc.c
==============================================================================
--- head/sys/kern/kern_tc.c	Tue Dec 19 10:02:09 2017	(r326972)
+++ head/sys/kern/kern_tc.c	Tue Dec 19 10:05:45 2017	(r326973)
@@ -1601,10 +1601,10 @@ pps_fetch(struct pps_fetch_args *fapi, struct pps_stat
 			tv.tv_usec = fapi->timeout.tv_nsec / 1000;
 			timo = tvtohz(&tv);
 		}
-		aseq = pps->ppsinfo.assert_sequence;
-		cseq = pps->ppsinfo.clear_sequence;
-		while (aseq == pps->ppsinfo.assert_sequence &&
-		    cseq == pps->ppsinfo.clear_sequence) {
+		aseq = atomic_load_int(&pps->ppsinfo.assert_sequence);
+		cseq = atomic_load_int(&pps->ppsinfo.clear_sequence);
+		while (aseq == atomic_load_int(&pps->ppsinfo.assert_sequence) &&
+		    cseq == atomic_load_int(&pps->ppsinfo.clear_sequence)) {
 			if (abi_aware(pps, 1) && pps->driver_mtx != NULL) {
 				if (pps->flags & PPSFLAG_MTX_SPIN) {
 					err = msleep_spin(pps, pps->driver_mtx,