Mesa (main): util/libsync: Fix timeout handling if poll() wakes up early

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Module: Mesa
Branch: main
Commit: df92a13a270bea95f5c5260ee5de0c5b776f5131
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=df92a13a270bea95f5c5260ee5de0c5b776f5131

Author: Jesse Natalie <jenatali at microsoft.com>
Date:   Tue Nov  2 10:10:01 2021 -0700

util/libsync: Fix timeout handling if poll() wakes up early

Check how long poll waited, and use a smaller timeout on the next
iteration through the loop.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12268>

---

 src/util/libsync.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/util/libsync.h b/src/util/libsync.h
index 1c9303c174a..0cb895a75d3 100644
--- a/src/util/libsync.h
+++ b/src/util/libsync.h
@@ -36,6 +36,7 @@
 #include <sys/ioctl.h>
 #include <sys/poll.h>
 #include <unistd.h>
+#include <time.h>
 
 #if defined(__cplusplus)
 extern "C" {
@@ -102,12 +103,15 @@ static inline int sync_wait(int fd, int timeout)
 {
 	struct pollfd fds = {0};
 	int ret;
+	struct timespec poll_start, poll_end;
 
 	fds.fd = fd;
 	fds.events = POLLIN;
 
 	do {
+		clock_gettime(CLOCK_MONOTONIC, &poll_start);
 		ret = poll(&fds, 1, timeout);
+		clock_gettime(CLOCK_MONOTONIC, &poll_end);
 		if (ret > 0) {
 			if (fds.revents & (POLLERR | POLLNVAL)) {
 				errno = EINVAL;
@@ -118,6 +122,8 @@ static inline int sync_wait(int fd, int timeout)
 			errno = ETIME;
 			return -1;
 		}
+		timeout -= (poll_end.tv_sec - poll_start.tv_sec) * 1000 +
+			(poll_end.tv_nsec - poll_end.tv_nsec) / 1000000;
 	} while (ret == -1 && (errno == EINTR || errno == EAGAIN));
 
 	return ret;