linux-imx

ftrace, kprobes: Fix a deadlock on ftrace_regex_lock

Fix a deadlock on ftrace_regex_lock which happens when setting
an enable_event trigger on dynamic kprobe event as below.

----
sh-2.05b# echo p vfs_symlink > kprobe_events
sh-2.05b# echo vfs_symlink:enable_event:kprobes:p_vfs_symlink_0 > set_ftrace_filter

=============================================
[ INFO: possible recursive locking detected ]
3.9.0+ #35 Not tainted
---------------------------------------------
sh/72 is trying to acquire lock:
 (ftrace_regex_lock){+.+.+.}, at: [<ffffffff810ba6c1>] ftrace_set_hash+0x81/0x1f0

but task is already holding lock:
 (ftrace_regex_lock){+.+.+.}, at: [<ffffffff810b7cbd>] ftrace_regex_write.isra.29.part.30+0x3d/0x220

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(ftrace_regex_lock);
  lock(ftrace_regex_lock);

 *** DEADLOCK ***
----

To fix that, this introduces a finer regex_lock for each ftrace_ops.
ftrace_regex_lock is too big of a lock which protects all
filter/notrace_hash operations, but it doesn't need to be a global
lock after supporting multiple ftrace_ops because each ftrace_ops
has its own filter/notrace_hash.

Link: http://lkml.kernel.org/r/20130509054417.30398.84254.stgit@mhiramat-M0-7522

Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
[ Added initialization flag and automate mutex initialization for
  non ftrace.c ftrace_probes. ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>