tracing: Make tracer_flags use the right set_flag callback

When I was updating the ftrace_stress test of ltp. I encountered
a strange phenomemon, excute following steps:

echo nop > /sys/kernel/debug/tracing/current_tracer
echo 0 > /sys/kernel/debug/tracing/options/funcgraph-cpu
bash: echo: write error: Invalid argument

check dmesg:
[ 1024.903855] nop_test_refuse flag set to 0: we refuse.Now cat trace_options to see the result

The reason is that the trace option test will randomly setup trace
option under tracing/options no matter what the current_tracer is.
but the set_tracer_option is always using the set_flag callback
from the current_tracer. This patch adds a pointer to tracer_flags
and make it point to the tracer it belongs to. When the option is
setup, the set_flag of the right tracer will be used no matter
what the the current_tracer is.

And the old dummy_tracer_flags is used for all the tracers which
doesn't have a tracer_flags, having issue to use it to save the
pointer of a tracer. So remove it and use dynamic dummy tracer_flags
for tracers needing a dummy tracer_flags, as a result, there are no
tracers sharing tracer_flags, so remove the check code.

And save the current tracer to trace_option_dentry seems not good as
it may waste mem space when mount the debug/trace fs more than one time.

Link: http://lkml.kernel.org/r/1457444222-8654-1-git-send-email-chuhu@redhat.com

Signed-off-by: Chunyu Hu <chuhu@redhat.com>
[ Fixed up function tracer options to work with the change ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 21 insertions, 14 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d9293402ee68..b401a1892dc6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -74,11 +74,6 @@ static struct tracer_opt dummy_tracer_opt[] = {
         { }
 };
 
-static struct tracer_flags dummy_tracer_flags = {
-        .val = 0,
-        .opts = dummy_tracer_opt
-};
-
 static int
 dummy_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
 {
@@ -1258,12 +1253,20 @@ int __init register_tracer(struct tracer *type)
 
         if (!type->set_flag)
                 type->set_flag = &dummy_set_flag;
-        if (!type->flags)
-                type->flags = &dummy_tracer_flags;
-        else
+        if (!type->flags) {
+                /*allocate a dummy tracer_flags*/
+                type->flags = kmalloc(sizeof(*type->flags), GFP_KERNEL);
+                if (!type->flags)
+                        return -ENOMEM;
+                type->flags->val = 0;
+                type->flags->opts = dummy_tracer_opt;
+        } else
                 if (!type->flags->opts)
                         type->flags->opts = dummy_tracer_opt;
 
+        /* store the tracer for __set_tracer_option */
+        type->flags->trace = type;
+
         ret = run_tracer_selftest(type);
         if (ret < 0)
                 goto out;
@@ -3505,7 +3508,7 @@ static int __set_tracer_option(struct trace_array *tr,
                                struct tracer_flags *tracer_flags,
                                struct tracer_opt *opts, int neg)
 {
-        struct tracer *trace = tr->current_trace;
+        struct tracer *trace = tracer_flags->trace;
         int ret;
 
         ret = trace->set_flag(tr, tracer_flags->val, opts->bit, !neg);
@@ -6391,11 +6394,8 @@ create_trace_option_files(struct trace_array *tr, struct tracer *tracer)
                 return;
 
         for (i = 0; i < tr->nr_topts; i++) {
-                /*
-                 * Check if these flags have already been added.
-                 * Some tracers share flags.
-                 */
-                if (tr->topts[i].tracer->flags == tracer->flags)
+                /* Make sure there's no duplicate flags. */
+                if (WARN_ON_ONCE(tr->topts[i].tracer->flags == tracer->flags))
                         return;
         }
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8414fa40bf27..b4cae47f283e 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -345,6 +345,7 @@ struct tracer_opt {
 struct tracer_flags {
         u32                     val;
         struct tracer_opt       *opts;
+        struct tracer           *trace;
 };
 
 /* Makes more easy to define a tracer opt */
diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index fcd41a166405..5a095c2e4b69 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -219,6 +219,8 @@ static void tracing_stop_function_trace(struct trace_array *tr)
         unregister_ftrace_function(tr->ops);
 }
 
+static struct tracer function_trace;
+
 static int
 func_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
 {
@@ -228,6 +230,10 @@ func_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
                 if (!!set == !!(func_flags.val & TRACE_FUNC_OPT_STACK))
                         break;
 
+                /* We can change this flag when not running. */
+                if (tr->current_trace != &function_trace)
+                        break;
+
                 unregister_ftrace_function(tr->ops);
 
                 if (set) {