linux-kernel - [PATCH 28/37] perf machine: Fix machine__findnew_module

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Date:	Thu, 19 Nov 2015 14:53:14 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 28/37] perf machine: Fix machine__findnew_module_map to put dso

From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Fix machine__findnew_module_map to drop the reference to the dso because
it is already referenced by both machine__findnew_module_dso() and
map__new2().

Refcnt debugger shows:

  ==== [1] ====
  Unreclaimed dso: 0x1ffd980
  Refcount +1 => 1 at
    ./perf(dso__new+0x1ff) [0x4a62df]
    ./perf(__dsos__addnew+0x29) [0x4a6e19]
    ./perf() [0x4b8b91]
    ./perf(modules__parse+0xfc) [0x4a9d5c]
    ./perf() [0x4b8460]
    ./perf(machine__create_kernel_maps+0x150) [0x4bb550]
    ./perf(machine__new_host+0xfa) [0x4bb75a]
    ./perf(init_probe_symbol_maps+0x93) [0x506623]
    ./perf() [0x455ffa]
    ./perf(cmd_probe+0x6c) [0x4566bc]
    ./perf() [0x47abc5]
    ./perf(main+0x610) [0x421f90]
    /lib64/libc.so.6(__libc_start_main+0xf5) [0x7f1345a8eaf5]
    ./perf() [0x4220a9]

This map_groups__insert(0x4b8b91) already gets a reference to the new
dso:

  ----
  eu-addr2line -e ./perf -f 0x4b8b91
  map_groups__insert inlined at util/machine.c:586 in
  machine__create_module
  util/map.h:207
  ----

So this dso refcnt will be released when map_groups gets released.

  [snip]
  Refcount +1 => 2 at
    ./perf(dso__get+0x34) [0x4a65f4]
    ./perf() [0x4b8b35]
    ./perf(modules__parse+0xfc) [0x4a9d5c]
    ./perf() [0x4b8460]
    ./perf(machine__create_kernel_maps+0x150) [0x4bb550]
    ./perf(machine__new_host+0xfa) [0x4bb75a]
    ./perf(init_probe_symbol_maps+0x93) [0x506623]
    ./perf() [0x455ffa]
    ./perf(cmd_probe+0x6c) [0x4566bc]
    ./perf() [0x47abc5]
    ./perf(main+0x610) [0x421f90]
    /lib64/libc.so.6(__libc_start_main+0xf5) [0x7f1345a8eaf5]
    ./perf() [0x4220a9]

Here, machine__findnew_module_dso(0x4b8b35) gets the dso (and stores it
in a local variable):

  ----
  # eu-addr2line -e ./perf -f 0x4b8b35
  machine__findnew_module_dso inlined at util/machine.c:578 in
  machine__create_module
  util/machine.c:514
  ----

  Refcount +1 => 3 at
    ./perf(dso__get+0x34) [0x4a65f4]
    ./perf(map__new2+0x76) [0x4be1c6]
    ./perf() [0x4b8b4f]
    ./perf(modules__parse+0xfc) [0x4a9d5c]
    ./perf() [0x4b8460]
    ./perf(machine__create_kernel_maps+0x150) [0x4bb550]
    ./perf(machine__new_host+0xfa) [0x4bb75a]
    ./perf(init_probe_symbol_maps+0x93) [0x506623]
    ./perf() [0x455ffa]
    ./perf(cmd_probe+0x6c) [0x4566bc]
    ./perf() [0x47abc5]
    ./perf(main+0x610) [0x421f90]
    /lib64/libc.so.6(__libc_start_main+0xf5) [0x7f1345a8eaf5]
    ./perf() [0x4220a9]

But also map__new2() gets the dso which will be put when the map is
released.

So, we have to drop the constructor reference obtained in
machine__findnew_module_dso().

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/20151118064035.30709.58824.stgit@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/machine.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 0b4a05c14204..7f5071a4d9aa 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -565,7 +565,7 @@ struct map *machine__findnew_module_map(struct machine *machine, u64 start,
 					const char *filename)
 {
 	struct map *map = NULL;
-	struct dso *dso;
+	struct dso *dso = NULL;
 	struct kmod_path m;
 
 	if (kmod_path__parse_name(&m, filename))
@@ -589,6 +589,8 @@ struct map *machine__findnew_module_map(struct machine *machine, u64 start,
 	/* Put the map here because map_groups__insert alread got it */
 	map__put(map);
 out:
+	/* put the dso here, corresponding to  machine__findnew_module_dso */
+	dso__put(dso);
 	free(m.name);
 	return map;
 }
-- 
2.1.0

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