tracing: Turn event/id->i_private into call->event.type

event_id_read() is racy, ftrace_event_call can be already freed
by trace_remove_event_call() callers.

Change event_create_dir() to pass "data = call->event.type", this
is all event_id_read() needs. ftrace_event_id_fops no longer needs
tracing_open_generic().

We add the new helper, event_file_data(), to read ->i_private, it
will have more users.

Note: currently ACCESS_ONCE() and "id != 0" check are not needed,
but we are going to change event_remove/rmdir to clear ->i_private.

Link: http://lkml.kernel.org/r/20130726172532.GA3605@redhat.com

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 13 insertions, 5 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 898f868833f2..c2d13c528c3c 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -409,6 +409,11 @@ static void put_system(struct ftrace_subsystem_dir *dir)
         mutex_unlock(&event_mutex);
 }
 
+static void *event_file_data(struct file *filp)
+{
+        return ACCESS_ONCE(file_inode(filp)->i_private);
+}
+
 /*
  * Open and update trace_array ref count.
  * Must have the current trace_array passed to it.
@@ -946,14 +951,18 @@ static int trace_format_open(struct inode *inode, struct file *file)
 static ssize_t
 event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 {
-        struct ftrace_event_call *call = filp->private_data;
+        int id = (long)event_file_data(filp);
         char buf[32];
         int len;
 
         if (*ppos)
                 return 0;
 
-        len = sprintf(buf, "%d\n", call->event.type);
+        if (unlikely(!id))
+                return -ENODEV;
+
+        len = sprintf(buf, "%d\n", id);
+
         return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
 }
 
@@ -1240,7 +1249,6 @@ static const struct file_operations ftrace_event_format_fops = {
 };
 
 static const struct file_operations ftrace_event_id_fops = {
-        .open = tracing_open_generic,
         .read = event_id_read,
         .llseek = default_llseek,
 };
@@ -1488,8 +1496,8 @@ event_create_dir(struct dentry *parent,
 
 #ifdef CONFIG_PERF_EVENTS
         if (call->event.type && call->class->reg)
-                trace_create_file("id", 0444, file->dir, call,
-                                  id);
+                trace_create_file("id", 0444, file->dir,
+                                  (void *)(long)call->event.type, id);
 #endif
 
         /*