Use critical_enter/critical_exit around the time sensitive part of

this code to depessimize the worst case we've lived with silently and
uneventfully for the past 12 years. Add a comment about a refinement
for those needing more assurance of accuracy.

Fix ddb's show rtc command deadlock potential when debugging rtc code
by not taking the lock if we're in the debugger. If you need a thumb
to count the number of people that have encountered this, I'd be
surprised.

Submitted by:	bde

1 files changed, 12 insertions, 4 deletions

diff --git a/sys/x86/isa/atrtc.c b/sys/x86/isa/atrtc.c
index b42beac..c6a6f8c 100644
--- a/sys/x86/isa/atrtc.c
+++ b/sys/x86/isa/atrtc.c
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/clock.h>
 #include <sys/lock.h>
 #include <sys/mutex.h>
+#include <sys/kdb.h>
 #include <sys/kernel.h>
 #include <sys/module.h>
 #include <sys/proc.h>
@@ -52,8 +53,8 @@ __FBSDID("$FreeBSD$");
 #include <machine/intr_machdep.h>
 #include "clock_if.h"
 
-#define	RTC_LOCK	mtx_lock_spin(&clock_lock)
-#define	RTC_UNLOCK	mtx_unlock_spin(&clock_lock)
+#define	RTC_LOCK	do { if (!kdb_active) mtx_lock_spin(&clock_lock); } while (0)
+#define	RTC_UNLOCK	do { if (!kdb_active) mtx_unlock_spin(&clock_lock); } while (0)
 
 int	atrtcclock_disable = 0;
 
@@ -335,10 +336,16 @@ atrtc_gettime(device_t dev, struct timespec *ts)
 		return (EINVAL);
 	}
 
-	/* wait for time update to complete */
-	/* If RTCSA_TUP is zero, we have at least 244us before next update */
+	/*
+	 * wait for time update to complete
+	 * If RTCSA_TUP is zero, we have at least 244us before next update.
+	 * This is fast enough on most hardware, but a refinement would be
+	 * to make sure that no more than 240us pass after we start reading,
+	 * and try again if so.
+	 */
 	while (rtcin(RTC_STATUSA) & RTCSA_TUP)
 		continue;
+	critical_enter();
 	ct.nsec = 0;
 	ct.sec = readrtc(RTC_SEC);
 	ct.min = readrtc(RTC_MIN);
@@ -352,6 +359,7 @@ atrtc_gettime(device_t dev, struct timespec *ts)
 #else
 	ct.year += 2000;
 #endif
+	critical_exit();
 	/* Set dow = -1 because some clocks don't set it correctly. */
 	ct.dow = -1;
 	return (clock_ct_to_ts(&ct, ts));