From bc6f6b08dee5645770efb4b76186ded313f23752 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Fri, 26 Jul 2013 19:25:36 +0200
Subject: [PATCH] tracing: Change event_enable/disable_read() to verify
 i_private != NULL

tracing_open_generic_file() is racy, ftrace_event_file can be
already freed by rmdir or trace_remove_event_call().

Change event_enable_read() and event_disable_read() to read and
verify "file = i_private" under event_mutex.

This fixes nothing, but now we can change debugfs_remove("enable")
callers to nullify ->i_private and fix the the problem.

Link: http://lkml.kernel.org/r/20130726172536.GA3612@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>
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