[PATCH] cgroup: avoid false positive gcc-6 warning

[PATCH] cgroup: avoid false positive gcc-6 warning

[Arnd Bergmann]

When all subsystems are disabled, gcc notices that cgroup_subsys_enabled_key
is a zero-length array and that any access to it must be out of bounds:

In file included from ../include/linux/cgroup.h:19:0,
                 from ../kernel/cgroup.c:31:
../kernel/cgroup.c: In function 'cgroup_add_cftypes':
../kernel/cgroup.c:261:53: error: array subscript is above array bounds [-Werror=array-bounds]
  return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
                            ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
../include/linux/jump_label.h:271:40: note: in definition of macro 'static_key_enabled'
  static_key_count((struct static_key *)x) > 0;    \
                                        ^

We should never call the function in this particular case, so this is
not a bug. In order to silence the warning, this adds an explicit check
for the CGROUP_SUBSYS_COUNT==0 case.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 kernel/cgroup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 155c88470543..3348a36c3694 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -258,6 +258,9 @@ static int cgroup_addrm_files(struct cgroup_subsys_state *css,
  */
 static bool cgroup_ssid_enabled(int ssid)
 {
+	if (CGROUP_SUBSYS_COUNT == 0)
+		return 0;
+
 	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 }
 
-- 
2.7.0

Re: [PATCH] cgroup: avoid false positive gcc-6 warning

[kbuild test robot]

Hi Arnd,

[auto build test WARNING on cgroup/for-next]
[also build test WARNING on v4.5 next-20160314]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Arnd-Bergmann/cgroup-avoid-false-positive-gcc-6-warning/20160315-063927
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next


coccinelle warnings: (new ones prefixed by >>)

>> kernel/cgroup.c:262:9-10: WARNING: return of 0/1 in function 'cgroup_ssid_enabled' with return type bool

Please review and possibly fold the followup patch.

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[PATCH] cgroup: fix boolreturn.cocci warnings

[kbuild test robot]

kernel/cgroup.c:262:9-10: WARNING: return of 0/1 in function 'cgroup_ssid_enabled' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

CC: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
---

 cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -259,7 +259,7 @@ static int cgroup_addrm_files(struct cgr
 static bool cgroup_ssid_enabled(int ssid)
 {
 	if (CGROUP_SUBSYS_COUNT == 0)
-		return 0;
+		return false;
 
 	return static_key_enabled(cgroup_subsys_enabled_key[ssid]);
 }