[PATCH v2 6/6] tracing: Change remove_event_file_dir() to clear "d_subdirs"->i_private

[Oleg Nesterov <oleg@redhat.com>]

Change remove_event_file_dir() to clear ->i_private for every
file we are going to remove.

tracing_open_generic_file() and tracing_release_generic_file()
can go away, ftrace_enable_fops and ftrace_event_filter_fops()
use tracing_open_generic() but only to check tracing_disabled.

This fixes all races with event_remove() or instance_delete().
f_op->read/write/whatever can never use the freed file/call,
all event/* files were changed to check and use ->i_private
under event_mutex.

Note: this doesn't not fix other problems, event_remove() can
destroy the active ftrace_event_call, we need more changes but
those changes are completely orthogonal.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_events.c |   41 +++++++++--------------------------------
 1 files changed, 9 insertions(+), 32 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2a4f68a..1112fa0 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -428,42 +428,20 @@ static void *event_file_data(struct file *filp)
 
 static void remove_event_file_dir(struct ftrace_event_file *file)
 {
+	struct dentry *dir = file->dir;
+	struct dentry *child;
+
+	/* ->i_mutex is not needed, nobody can create/remove a file */
+	list_for_each_entry(child, &dir->d_subdirs, d_u.d_child)
+		child->d_inode->i_private = NULL;
+
 	list_del(&file->list);
-	debugfs_remove_recursive(file->dir);
+	debugfs_remove_recursive(dir);
 	remove_subsystem(file->system);
 	kmem_cache_free(file_cachep, file);
 }
 
 /*
- * Open and update trace_array ref count.
- * Must have the current trace_array passed to it.
- */
-static int tracing_open_generic_file(struct inode *inode, struct file *filp)
-{
-	struct ftrace_event_file *file = inode->i_private;
-	struct trace_array *tr = file->tr;
-	int ret;
-
-	if (trace_array_get(tr) < 0)
-		return -ENODEV;
-
-	ret = tracing_open_generic(inode, filp);
-	if (ret < 0)
-		trace_array_put(tr);
-	return ret;
-}
-
-static int tracing_release_generic_file(struct inode *inode, struct file *filp)
-{
-	struct ftrace_event_file *file = inode->i_private;
-	struct trace_array *tr = file->tr;
-
-	trace_array_put(tr);
-
-	return 0;
-}
-
-/*
  * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
  */
 static int
@@ -1277,10 +1255,9 @@ static const struct file_operations ftrace_set_event_fops = {
 };
 
 static const struct file_operations ftrace_enable_fops = {
-	.open = tracing_open_generic_file,
+	.open = tracing_open_generic,
 	.read = event_enable_read,
 	.write = event_enable_write,
-	.release = tracing_release_generic_file,
 	.llseek = default_llseek,
 };
 
-- 
1.5.5.1