perf core: Generalize max_stack sysctl handler

So that it can be used for other stack related knobs, such as the
upcoming one to tweak the max number of of contexts per stack sample.

In all those cases we can only change the value if there are no perf
sessions collecting stacks, so they need to grab that mutex, etc.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-8t3fk94wuzp8m2z1n4gc0s17@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 4 insertions, 3 deletions

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index b9325e7dcba1..7fc89939ede9 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -228,7 +228,8 @@ exit_put:
 int perf_event_max_stack_handler(struct ctl_table *table, int write,
                                  void __user *buffer, size_t *lenp, loff_t *ppos)
 {
-        int new_value = sysctl_perf_event_max_stack, ret;
+        int *value = table->data;
+        int new_value = *value, ret;
         struct ctl_table new_table = *table;
 
         new_table.data = &new_value;
@@ -240,7 +241,7 @@ int perf_event_max_stack_handler(struct ctl_table *table, int write,
         if (atomic_read(&nr_callchain_events))
                 ret = -EBUSY;
         else
-                sysctl_perf_event_max_stack = new_value;
+                *value = new_value;
 
         mutex_unlock(&callchain_mutex);
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c8b318663525..0ec6907a16b3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1149,7 +1149,7 @@ static struct ctl_table kern_table[] = {
         },
         {
                 .procname       = "perf_event_max_stack",
-                .data           = NULL, /* filled in by handler */
+                .data           = &sysctl_perf_event_max_stack,
                 .maxlen         = sizeof(sysctl_perf_event_max_stack),
                 .mode           = 0644,
                 .proc_handler   = perf_event_max_stack_handler,