[PATCH] perf trace: Fix potential u64 underflow in duration calculation

[Michael Petlan <mpetlan@redhat.com>]

Although it happens very rarely, in case of out-of-order events (i.e.
due to CPU migration when a syscall is executed), the calculation of
event duration might underflow and thus a bogus value is printed:

    2.804 ( 0.001 ms): :49553/49553 rt_sigaction(sig: QUIT, act: 0x7fff403ed6e0, oact: 0x7fff403ed780, sigsetsize: 8) = 0
    2.807 ( 0.001 ms): :49553/49553 rt_sigaction(sig: CHLD, act: 0x7fff403ed6e0, oact: 0x7fff403ed780, sigsetsize: 8) = 0
    2.815 (18446744073709.438 ms): :49553/49553 execve(filename: 0xbb173a30, argv: 0x55aabb171930, envp: 0x55aabb171120) = 0
    2.815 ( 0.534 ms): pwd/49553  ... [continued]: execve())                                           = 0

Check for possible underflow first and in case of a bogus value, do
not print it.

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
---
 tools/perf/builtin-trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
index f487fbaa0ad6..c9de6bb9b0ea 100644
--- a/tools/perf/builtin-trace.c
+++ b/tools/perf/builtin-trace.c
@@ -2956,7 +2956,7 @@ static int trace__sys_exit(struct trace *trace, struct evsel *evsel,
 		++trace->stats.vfs_getname;
 	}
 
-	if (ttrace->entry_time) {
+	if (ttrace->entry_time && sample->time > ttrace->entry_time) {
 		duration = sample->time - ttrace->entry_time;
 		if (trace__filter_duration(trace, duration))
 			goto out;
-- 
2.47.3