[PATCH] perf: Fix perf_event_{init,exit}_cpu stubs

[Florian Fainelli <f.fainelli@gmail.com>]

The original commit that introduced those stubs was already at fault,
but in the absence of a caller of perf_event_{init,exit}_cpu outside of
code that is compiled regardless of CONFIG_PERF_EVENTS, the build
failure cannot be observed. This was observed with the Android kernel to
produce a build failure similar to this:

    In file included from ./include/uapi/linux/posix_types.h:5,
                     from ./include/uapi/linux/types.h:14,
                     from ./include/linux/types.h:6,
                     from ./include/linux/limits.h:6,
                     from ./include/linux/kernel.h:7,
                     from ./include/linux/sched/mm.h:5,
                     from kernel/cpu.c:6:
    kernel/cpu.c: In function 'random_and_perf_prepare_fusion':
    ./include/linux/stddef.h:8:14: error: called object is not a function or function pointer
     #define NULL ((void *)0)
                  ^
    ./include/linux/perf_event.h:1607:29: note: in expansion of macro 'NULL'
     #define perf_event_init_cpu NULL
                                 ^~~~
    kernel/cpu.c:1686:2: note: in expansion of macro 'perf_event_init_cpu'
      perf_event_init_cpu(cpu);
      ^~~~~~~~~~~~~~~~~~~

Fixes: 00e16c3d68fc ("perf/core: Convert to hotplug state machine")
Reported-by: Anand Gore <anand.gore@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 include/linux/perf_event.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0031f7b4d9ab..592040e2398c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1678,8 +1678,15 @@ static struct device_attribute format_attr_##_name = __ATTR_RO(_name)
 int perf_event_init_cpu(unsigned int cpu);
 int perf_event_exit_cpu(unsigned int cpu);
 #else
-#define perf_event_init_cpu	NULL
-#define perf_event_exit_cpu	NULL
+static inline int perf_event_init_cpu(unsigned int cpu)
+{
+	return 0;
+}
+
+static inline int perf_event_exit_cpu(unsigned int cpu)
+{
+	return 0;
+}
 #endif
 
 extern void __weak arch_perf_update_userpage(struct perf_event *event,
-- 
2.25.1