[tip:perf/urgent] perf probe: Set pev->nargs to zero after freeing pev->args entries

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  df8350ed56a26f502a9636f37faf699a12ee906e
Gitweb:     https://git.kernel.org/tip/df8350ed56a26f502a9636f37faf699a12ee906e
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Thu, 18 Jul 2019 11:22:58 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 23 Jul 2019 09:04:25 -0300

perf probe: Set pev->nargs to zero after freeing pev->args entries

So that, when perf_add_probe_events() fails, like in:

  # perf probe icmp_rcv:64 "type=icmph->type"
  Failed to find 'icmph' in this function.
    Error: Failed to add events.
  Segmentation fault (core dumped)
  #

We don't segfault.

clear_perf_probe_event() was zeroing the whole pev, and since the switch
to zfree() for the members in the pev, that memset() was removed, which
left nargs with its original value, in the above case 1.

With the memset the same pev could be passed to clear_perf_probe_event()
multiple times, since all it would have would be zeroes, and free()
accepts zero, the loop would not happen and we would just memset it
again to zeroes.

Without it we got that segfault, so zero nargs to keep it like it was,
next cset will avoid calling clear_perf_probe_event() for the same pevs
in case of failure.

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Fixes: d8f9da240495 ("perf tools: Use zfree() where applicable")
Link: https://lkml.kernel.org/n/tip-802f2jypnwqsvyavvivs8464@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/probe-event.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 0c3b55d0617d..4acd3457d39d 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2219,6 +2219,7 @@ void clear_perf_probe_event(struct perf_probe_event *pev)
 			field = next;
 		}
 	}
+	pev->nargs = 0;
 	zfree(&pev->args);
 }