ftrace: Get a reference counter for the trace_array on filter files

The ftrace set_ftrace_filter and set_ftrace_notrace files are specific for
an instance now. They need to take a reference to the instance otherwise
there could be a race between accessing the files and deleting the instance.

It wasn't until the :mod: caching where these file operations started
referencing the trace_array directly.

Cc: stable@vger.kernel.org
Fixes: 673feb9d76ab3 ("ftrace: Add :mod: caching infrastructure to trace_array")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 62a50bf399d6365131158cb65c2fc4ea62526202..32c2eb167de0d6718f67a54ade450407c67cf367 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3540,21 +3540,22 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
        struct ftrace_hash *hash;
        struct list_head *mod_head;
        struct trace_array *tr = ops->private;
-       int ret = 0;
+       int ret = -ENOMEM;
 
        ftrace_ops_init(ops);
 
        if (unlikely(ftrace_disabled))
                return -ENODEV;
 
+       if (tr && trace_array_get(tr) < 0)
+               return -ENODEV;
+
        iter = kzalloc(sizeof(*iter), GFP_KERNEL);
        if (!iter)
-               return -ENOMEM;
+               goto out;
 
-       if (trace_parser_get_init(&iter->parser, FTRACE_BUFF_MAX)) {
-               kfree(iter);
-               return -ENOMEM;
-       }
+       if (trace_parser_get_init(&iter->parser, FTRACE_BUFF_MAX))
+               goto out;
 
        iter->ops = ops;
        iter->flags = flag;
@@ -3584,13 +3585,13 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
 
                if (!iter->hash) {
                        trace_parser_put(&iter->parser);
-                       kfree(iter);
-                       ret = -ENOMEM;
                        goto out_unlock;
                }
        } else
                iter->hash = hash;
 
+       ret = 0;
+
        if (file->f_mode & FMODE_READ) {
                iter->pg = ftrace_pages_start;
 
@@ -3602,7 +3603,6 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
                        /* Failed */
                        free_ftrace_hash(iter->hash);
                        trace_parser_put(&iter->parser);
-                       kfree(iter);
                }
        } else
                file->private_data = iter;
@@ -3610,6 +3610,13 @@ ftrace_regex_open(struct ftrace_ops *ops, int flag,
  out_unlock:
        mutex_unlock(&ops->func_hash->regex_lock);
 
+ out:
+       if (ret) {
+               kfree(iter);
+               if (tr)
+                       trace_array_put(tr);
+       }
+
        return ret;
 }
 
@@ -5037,6 +5044,8 @@ int ftrace_regex_release(struct inode *inode, struct file *file)
 
        mutex_unlock(&iter->ops->func_hash->regex_lock);
        free_ftrace_hash(iter->hash);
+       if (iter->tr)
+               trace_array_put(iter->tr);
        kfree(iter);
 
        return 0;