[RFC PATCH 1/4] tracing: Change remove_event_from_tracers() to clear d_subdirs->i_private

[Oleg Nesterov <oleg@redhat.com>]

Preparation to make the next patches more understandable.

The caller of trace_remove_event_call() is going to free call/files,
this means that every opened id/filter/enable/format file will use
the already freed memory via filp->private_data / inode->i_private.

Change remove_event_from_tracers() to clear ->i_private for every
child. This fixes nothing and even makes the crash more possible,
but this allows to fix the problem later.

Note: this doesn't affect instance_rmdir() paths. It has the similar
problems and they will be fixed separately.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_events.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 9d2b499..cbd1a57 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1534,6 +1534,14 @@ static void remove_subsystem(struct ftrace_subsystem_dir *dir)
 	}
 }
 
+static void invalidate_event_file(struct dentry *dir)
+{
+	struct dentry *child;
+	/* ->i_mutex is not needed, nodody can create/remove a file */
+	list_for_each_entry(child, &dir->d_subdirs, d_u.d_child)
+		child->d_inode->i_private = NULL;
+}
+
 static void remove_event_from_tracers(struct ftrace_event_call *call)
 {
 	struct ftrace_event_file *file;
@@ -1545,6 +1553,7 @@ static void remove_event_from_tracers(struct ftrace_event_call *call)
 			continue;
 
 		list_del(&file->list);
+		invalidate_event_file(file->dir);
 		debugfs_remove_recursive(file->dir);
 		remove_subsystem(file->system);
 		kmem_cache_free(file_cachep, file);
-- 
1.5.5.1