perf_event: Allocate children's perf_event_ctxp at the right time

In current code, children task will allocate memory for
'child->perf_event_ctxp' if the parent is counted, we can
do it only if the parent allowed children inherit it.

It can save memory and reduce overhead.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <4B1F19A8.5040805@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 2b06c45bfba949d26727b893cceed3bfc1550eb4..77641ae6b23fa1f581e833b28af3a8d5a31fb2c3 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5083,7 +5083,7 @@ again:
  */
 int perf_event_init_task(struct task_struct *child)
 {
-       struct perf_event_context *child_ctx, *parent_ctx;
+       struct perf_event_context *child_ctx = NULL, *parent_ctx;
        struct perf_event_context *cloned_ctx;
        struct perf_event *event;
        struct task_struct *parent = current;
@@ -5098,20 +5098,6 @@ int perf_event_init_task(struct task_struct *child)
        if (likely(!parent->perf_event_ctxp))
                return 0;
 
-       /*
-        * This is executed from the parent task context, so inherit
-        * events that have been marked for cloning.
-        * First allocate and initialize a context for the child.
-        */
-
-       child_ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
-       if (!child_ctx)
-               return -ENOMEM;
-
-       __perf_event_init_context(child_ctx, child);
-       child->perf_event_ctxp = child_ctx;
-       get_task_struct(child);
-
        /*
         * If the parent's context is a clone, pin it so it won't get
         * swapped under us.
@@ -5142,6 +5128,26 @@ int perf_event_init_task(struct task_struct *child)
                        continue;
                }
 
+               if (!child->perf_event_ctxp) {
+                       /*
+                        * This is executed from the parent task context, so
+                        * inherit events that have been marked for cloning.
+                        * First allocate and initialize a context for the
+                        * child.
+                        */
+
+                       child_ctx = kzalloc(sizeof(struct perf_event_context),
+                                           GFP_KERNEL);
+                       if (!child_ctx) {
+                               ret = -ENOMEM;
+                               goto exit;
+                       }
+
+                       __perf_event_init_context(child_ctx, child);
+                       child->perf_event_ctxp = child_ctx;
+                       get_task_struct(child);
+               }
+
                ret = inherit_group(event, parent, parent_ctx,
                                             child, child_ctx);
                if (ret) {
@@ -5170,6 +5176,7 @@ int perf_event_init_task(struct task_struct *child)
                get_ctx(child_ctx->parent_ctx);
        }
 
+exit:
        mutex_unlock(&parent_ctx->mutex);
 
        perf_unpin_context(parent_ctx);