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Use critical_enter/critical_exit around the time sensitive part of

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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
This commit is contained in:
Warner Losh 2013-02-21 15:35:48 +00:00
parent c43b22be02
commit 22e61bc2c1
1 changed files with 12 additions and 4 deletions
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16
sys/x86/isa/atrtc.c
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@ -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));