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, 14 insertions, 5 deletions

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 713a2cac4881..443b25b43b4f 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -32,7 +32,7 @@ enum {
 
 static int trace_type __read_mostly;
 
-static int save_lat_flag;
+static int save_flags;
 
 static void stop_irqsoff_tracer(struct trace_array *tr, int graph);
 static int start_irqsoff_tracer(struct trace_array *tr, int graph);
@@ -558,8 +558,11 @@ static void stop_irqsoff_tracer(struct trace_array *tr, int graph)
 
 static void __irqsoff_tracer_init(struct trace_array *tr)
 {
-        save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
-        trace_flags |= TRACE_ITER_LATENCY_FMT;
+        save_flags = trace_flags;
+
+        /* non overwrite screws up the latency tracers */
+        set_tracer_flag(TRACE_ITER_OVERWRITE, 1);
+        set_tracer_flag(TRACE_ITER_LATENCY_FMT, 1);
 
         tracing_max_latency = 0;
         irqsoff_trace = tr;
@@ -573,10 +576,13 @@ static void __irqsoff_tracer_init(struct trace_array *tr)
 
 static void irqsoff_tracer_reset(struct trace_array *tr)
 {
+        int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
+        int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+
         stop_irqsoff_tracer(tr, is_graph());
 
-        if (!save_lat_flag)
-                trace_flags &= ~TRACE_ITER_LATENCY_FMT;
+        set_tracer_flag(TRACE_ITER_LATENCY_FMT, lat_flag);
+        set_tracer_flag(TRACE_ITER_OVERWRITE, overwrite_flag);
 }
 
 static void irqsoff_tracer_start(struct trace_array *tr)
@@ -609,6 +615,7 @@ static struct tracer irqsoff_tracer __read_mostly =
         .print_line     = irqsoff_print_line,
         .flags          = &tracer_flags,
         .set_flag       = irqsoff_set_flag,
+        .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
         .selftest    = trace_selftest_startup_irqsoff,
 #endif
@@ -642,6 +649,7 @@ static struct tracer preemptoff_tracer __read_mostly =
         .print_line     = irqsoff_print_line,
         .flags          = &tracer_flags,
         .set_flag       = irqsoff_set_flag,
+        .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
         .selftest    = trace_selftest_startup_preemptoff,
 #endif
@@ -677,6 +685,7 @@ static struct tracer preemptirqsoff_tracer __read_mostly =
         .print_line     = irqsoff_print_line,
         .flags          = &tracer_flags,
         .set_flag       = irqsoff_set_flag,
+        .flag_changed   = trace_keep_overwrite,
 #ifdef CONFIG_FTRACE_SELFTEST
         .selftest    = trace_selftest_startup_preemptirqsoff,
 #endif