[PATCH 5/5] perf probe: Clear probe_trace_event when add_probe_trace_event() fails

[Arnaldo Carvalho de Melo]

From: Wang Nan <wangnan0@xxxxxxxxxx>

When probing with a glob, errors in add_probe_trace_event() won't be
passed to debuginfo__find_trace_events() because it would be modified by
probe_point_search_cb(). It causes a segfault if perf fails to find an
argument for a probe point matched by the glob. For example:

  # ./perf probe -v -n 'SyS_dup? oldfd'
  probe-definition(0): SyS_dup? oldfd
  symbol:SyS_dup? file:(null) line:0 offset:0 return:0 lazy:(null)
  parsing arg: oldfd into oldfd
  1 arguments
  Looking at the vmlinux_path (7 entries long)
  Using /lib/modules/4.3.0-rc4+/build/vmlinux for symbols
  Open Debuginfo file: /lib/modules/4.3.0-rc4+/build/vmlinux
  Try to find probe point from debuginfo.
  Matched function: SyS_dup3
  found inline addr: 0xffffffff812095c0
  Probe point found: SyS_dup3+0
  Searching 'oldfd' variable in context.
  Converting variable oldfd into trace event.
  oldfd type is long int.
  found inline addr: 0xffffffff812096d4
  Probe point found: SyS_dup2+36
  Searching 'oldfd' variable in context.
  Failed to find 'oldfd' in this function.
  Matched function: SyS_dup3
  Probe point found: SyS_dup3+0
  Searching 'oldfd' variable in context.
  Converting variable oldfd into trace event.
  oldfd type is long int.
  Matched function: SyS_dup2
  Probe point found: SyS_dup2+0
  Searching 'oldfd' variable in context.
  Converting variable oldfd into trace event.
  oldfd type is long int.
  Found 4 probe_trace_events.
  Opening /sys/kernel/debug/tracing//kprobe_events write=1
  Writing event: p:probe/SyS_dup3 _text+2135488 oldfd=%di:s64
  Segmentation fault (core dumped)
  #

This patch ensures that add_probe_trace_event() doesn't touches
tf->ntevs and tf->tevs if those functions fail.

After the patch:

  # perf probe  'SyS_dup? oldfd'
  Failed to find 'oldfd' in this function.
  Added new events:
    probe:SyS_dup3       (on SyS_dup? with oldfd)
    probe:SyS_dup3_1     (on SyS_dup? with oldfd)
    probe:SyS_dup2       (on SyS_dup? with oldfd)

  You can now use it in all perf tools, such as:

	perf record -e probe:SyS_dup2 -aR sleep 1

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Link: http://lkml.kernel.org/r/1447417761-156094-3-git-send-email-wangnan0@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/probe-finder.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 63993d7e0fac..05012bb178d7 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1183,7 +1183,7 @@ static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
 			container_of(pf, struct trace_event_finder, pf);
 	struct perf_probe_point *pp = &pf->pev->point;
 	struct probe_trace_event *tev;
-	struct perf_probe_arg *args;
+	struct perf_probe_arg *args = NULL;
 	int ret, i;
 
 	/* Check number of tevs */
@@ -1198,19 +1198,23 @@ static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
 	ret = convert_to_trace_point(&pf->sp_die, tf->mod, pf->addr,
 				     pp->retprobe, pp->function, &tev->point);
 	if (ret < 0)
-		return ret;
+		goto end;
 
 	tev->point.realname = strdup(dwarf_diename(sc_die));
-	if (!tev->point.realname)
-		return -ENOMEM;
+	if (!tev->point.realname) {
+		ret = -ENOMEM;
+		goto end;
+	}
 
 	pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
 		 tev->point.offset);
 
 	/* Expand special probe argument if exist */
 	args = zalloc(sizeof(struct perf_probe_arg) * MAX_PROBE_ARGS);
-	if (args == NULL)
-		return -ENOMEM;
+	if (args == NULL) {
+		ret = -ENOMEM;
+		goto end;
+	}
 
 	ret = expand_probe_args(sc_die, pf, args);
 	if (ret < 0)
@@ -1234,6 +1238,10 @@ static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
 	}
 
 end:
+	if (ret) {
+		clear_probe_trace_event(tev);
+		tf->ntevs--;
+	}
 	free(args);
 	return ret;
 }
-- 
2.1.0

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