tracing: Prevent buffer overwrite disabled for latency tracers

The latency tracers require the buffers to be in overwrite mode,
otherwise they get screwed up. Force the buffers to stay in overwrite
mode when latency tracers are enabled.

Added a flag_changed() method to the tracer structure to allow
the tracers to see what flags are being changed, and also be able
to prevent the change from happing.

Cc: stable@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 57d7e5397d56..2081971367ea 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -283,11 +283,15 @@ struct tracer {
         enum print_line_t       (*print_line)(struct trace_iterator *iter);
         /* If you handled the flag setting, return 0 */
         int                     (*set_flag)(u32 old_flags, u32 bit, int set);
+        /* Return 0 if OK with change, else return non-zero */
+        int                     (*flag_changed)(struct tracer *tracer,
+                                                u32 mask, int set);
         struct tracer           *next;
         struct tracer_flags     *flags;
         bool                    print_max;
         bool                    use_max_tr;
         bool                    allocated_snapshot;
+        bool                    enabled;
 };
 
 
@@ -943,6 +947,8 @@ extern const char *__stop___trace_bprintk_fmt[];
 
 void trace_printk_init_buffers(void);
 void trace_printk_start_comm(void);
+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set);
+int set_tracer_flag(unsigned int mask, int enabled);
 
 #undef FTRACE_ENTRY
 #define FTRACE_ENTRY(call, struct_name, id, tstruct, print, filter)     \