tracing/filters: add filter_mutex to protect filter predicates

This patch adds a filter_mutex to prevent the filter predicates from
being accessed concurrently by various external functions.

It's based on a previous patch by Li Zefan:
        "[PATCH 7/7] tracing/filters: make filter preds RCU safe"

v2 changes:

- fixed wrong value returned in a add_subsystem_pred() failure case
  noticed by Li Zefan.

[ Impact: fix trace filter corruption/crashes on parallel access ]

Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: paulmck@linux.vnet.ibm.com
LKML-Reference: <1239946028.6639.13.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 1137f951be42..64f9d6d2735b 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -488,7 +488,7 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 
         trace_seq_init(s);
 
-        filter_print_preds(call->preds, call->n_preds, s);
+        filter_print_preds(call, s);
         r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
 
         kfree(s);
@@ -558,7 +558,7 @@ subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 
         trace_seq_init(s);
 
-        filter_print_preds(system->preds, system->n_preds, s);
+        filter_print_subsystem_preds(system, s);
         r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
 
         kfree(s);