[v2,4/4] ibacm: Use MONOTONIC time base to avoid timer expiration issues

Commit Message

Michael J. Ruhl Nov. 13, 2017, 9:25 p.m. UTC

From: Michael J. Ruhl <[e-mail]>

The event_wait() function uses the CLOCK_REALTIME time base for
calculating expiration times (default time base for gettimeofday()).

Using the CLOCK_REALTIME time base can introduce incorrect expiration
timeout calculations if the REALTIME clock changes, making a timeout
too long (possibly hours or days), or too short.

Update time base usage to the CLOCK_MONOTONIC time base to avoid time
change issues.

Reviewed-by: Mike Marciniszyn <[e-mail]>
Signed-off-by: Michael J. Ruhl <[e-mail]>
---
 ibacm/linux/osd.h |   20 +++++++++++---------
 1 files changed, 11 insertions(+), 9 deletions(-)


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Comments

Jason Gunthorpe Nov. 14, 2017, 3:04 a.m. UTC | #1

On Mon, Nov 13, 2017 at 04:25:04PM -0500, Michael J. Ruhl wrote:

Sorry, noticed a few more wonky things:

>  #define event_signal(e)	pthread_cond_signal(&(e)->cond)
>  #define ONE_SEC_IN_NSEC  1000000000

That should be 1000000000ULL so math doesn't accidental truncate

> +	clock_gettime(CLOCK_MONOTONIC, &wait);
> +	wait.tv_sec = wait.tv_sec + ((unsigned) timeout) / 1000;
> +	wait.tv_nsec = (wait.tv_nsec + (((unsigned) timeout) % 1000) * 1000000);

Why the odd casts to (unsigned) ? That should be (unsigned int)

> -	return (uint64_t) curtime.tv_sec * 1000000 + (uint64_t) curtime.tv_usec;
> +	struct timespec t;
> +	clock_gettime(CLOCK_MONOTONIC, &t);
> +	return ((uint64_t)t.tv_sec * ONE_SEC_IN_NSEC + (uint64_t)t.tv_nsec) / 1000;

These casts to uint64_t are also wrong, time is technically
signed. The change to ONE_SEC_IN_NSEC should remove the need
for the casting.

Jason
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Patch

diff --git a/ibacm/linux/osd.h b/ibacm/linux/osd.h
index d6cbb8f..1901a89 100644
--- a/ibacm/linux/osd.h
+++ b/ibacm/linux/osd.h
@@ -88,20 +88,23 @@  typedef struct { volatile int val; } atomic_t;
 typedef struct { pthread_cond_t cond; pthread_mutex_t mutex; } event_t;
 static inline void event_init(event_t *e)
 {
-	pthread_cond_init(&e->cond, NULL);
+	pthread_condattr_t attr;
+
+	pthread_condattr_init(&attr);
+	pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
+	pthread_cond_init(&e->cond, &attr);
 	pthread_mutex_init(&e->mutex, NULL);
 }
 #define event_signal(e)	pthread_cond_signal(&(e)->cond)
 #define ONE_SEC_IN_NSEC  1000000000
 static inline int event_wait(event_t *e, int timeout)
 {
-	struct timeval curtime;
 	struct timespec wait;
 	int ret;
 
-	gettimeofday(&curtime, NULL);
-	wait.tv_sec = curtime.tv_sec + ((unsigned) timeout) / 1000;
-	wait.tv_nsec = (curtime.tv_usec + (((unsigned) timeout) % 1000) * 1000) * 1000;
+	clock_gettime(CLOCK_MONOTONIC, &wait);
+	wait.tv_sec = wait.tv_sec + ((unsigned) timeout) / 1000;
+	wait.tv_nsec = (wait.tv_nsec + (((unsigned) timeout) % 1000) * 1000000);
 	if (wait.tv_nsec > ONE_SEC_IN_NSEC) {
 		wait.tv_sec++;
 		wait.tv_nsec -= ONE_SEC_IN_NSEC;
@@ -114,10 +117,9 @@  static inline int event_wait(event_t *e, int timeout)
 
 static inline uint64_t time_stamp_us(void)
 {
-	struct timeval curtime;
-	timerclear(&curtime);
-	gettimeofday(&curtime, NULL);
-	return (uint64_t) curtime.tv_sec * 1000000 + (uint64_t) curtime.tv_usec;
+	struct timespec t;
+	clock_gettime(CLOCK_MONOTONIC, &t);
+	return ((uint64_t)t.tv_sec * ONE_SEC_IN_NSEC + (uint64_t)t.tv_nsec) / 1000;
 }
 
 #define time_stamp_ms()  (time_stamp_us() / (uint64_t) 1000)