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From 81747ac6d3e846d1955edaa94dee9065e541b7d8 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Mon, 7 Sep 2015 13:04:39 +0200
Subject: [PATCH gnumach] kern: use proper memory fences when handling the
mapped time
* include/mach/time_value.h (struct mapped_time_value): Adjust comment.
* kern/mach_clock.c (mtime): Likewise. Also make it volatile.
(update_mapped_time): Use full hardware barriers.
(read_mapped_time): New macro with proper fences.
(record_time_stamp, host_get_time): Use the new macro.
---
include/mach/time_value.h | 2 ++
kern/mach_clock.c | 33 ++++++++++++++++++---------------
2 files changed, 20 insertions(+), 15 deletions(-)
diff --git a/include/mach/time_value.h b/include/mach/time_value.h
index 61be581..0dfe382 100644
--- a/include/mach/time_value.h
+++ b/include/mach/time_value.h
@@ -84,7 +84,9 @@ typedef struct time_value time_value_t;
* Read this mapped value with
* do {
* secs = mtime->seconds;
+ * __sync_synchronize();
* usecs = mtime->microseconds;
+ * __sync_synchronize();
* } while (secs != mtime->check_seconds);
*/
diff --git a/kern/mach_clock.c b/kern/mach_clock.c
index 2bcd232..dba2320 100644
--- a/kern/mach_clock.c
+++ b/kern/mach_clock.c
@@ -85,26 +85,36 @@ int bigadj = 1000000; /* adjust 10*tickadj if adjustment
* This update protocol, with a check value, allows
* do {
* secs = mtime->seconds;
+ * __sync_synchronize();
* usecs = mtime->microseconds;
+ * __sync_synchronize();
* } while (secs != mtime->check_seconds);
- * to read the time correctly. (On a multiprocessor this assumes
- * that processors see each other's writes in the correct order.
- * We have to insert write fence operations.) FIXME
+ * to read the time correctly.
*/
-mapped_time_value_t *mtime = 0;
+volatile mapped_time_value_t *mtime = 0;
#define update_mapped_time(time) \
MACRO_BEGIN \
if (mtime != 0) { \
mtime->check_seconds = (time)->seconds; \
- asm volatile("":::"memory"); \
+ __sync_synchronize(); \
mtime->microseconds = (time)->microseconds; \
- asm volatile("":::"memory"); \
+ __sync_synchronize(); \
mtime->seconds = (time)->seconds; \
} \
MACRO_END
+#define read_mapped_time(time) \
+MACRO_BEGIN \
+ do { \
+ time->seconds = mtime->seconds; \
+ __sync_synchronize(); \
+ time->microseconds = mtime->microseconds; \
+ __sync_synchronize(); \
+ } while (time->seconds != mtime->check_seconds); \
+MACRO_END
+
decl_simple_lock_data(, timer_lock) /* lock for ... */
timer_elt_data_t timer_head; /* ordered list of timeouts */
/* (doubles as end-of-list) */
@@ -395,10 +405,7 @@ clock_boottime_update(struct time_value *new_time)
void
record_time_stamp (time_value_t *stamp)
{
- do {
- stamp->seconds = mtime->seconds;
- stamp->microseconds = mtime->microseconds;
- } while (stamp->seconds != mtime->check_seconds);
+ read_mapped_time(stamp);
time_value_add(stamp, &clock_boottime_offset);
}
@@ -425,11 +432,7 @@ host_get_time(host, current_time)
if (host == HOST_NULL)
return(KERN_INVALID_HOST);
- do {
- current_time->seconds = access_once(mtime->seconds);
- current_time->microseconds = access_once(mtime->microseconds);
- } while (current_time->seconds != access_once(mtime->check_seconds));
-
+ read_mapped_time(current_time);
return (KERN_SUCCESS);
}
--
2.1.4
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