[PATCH v13 01/20] tracing: fgraph: Fix to add new fgraph_ops to array after ftrace_startup_subops()

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhira...@kernel.org>

Since the register_ftrace_graph() assigns a new fgraph_ops to
fgraph_array before registring it by ftrace_startup_subops(), the new
fgraph_ops can be used in function_graph_enter().

In most cases, it is still OK because those fgraph_ops's hashtable is
already initialized by ftrace_set_filter*() etc.

But if a user registers a new fgraph_ops which does not initialize the
hash list, ftrace_ops_test() in function_graph_enter() causes a NULL
pointer dereference BUG because fgraph_ops->ops.func_hash is NULL.

This can be reproduced by the below commands because function profiler's
fgraph_ops does not initialize the hash list;

 # cd /sys/kernel/tracing
 # echo function_graph > current_tracer
 # echo 1 > function_profile_enabled

To fix this problem, add a new fgraph_ops to fgraph_array after
ftrace_startup_subops(). Thus, until the new fgraph_ops is initialized,
we will see fgraph_stub on the corresponding fgraph_array entry.

Fixes: c132be2c4fcc ("function_graph: Have the instances use their own 
ftrace_ops for filtering")
Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
 kernel/trace/fgraph.c |   31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index d1d5ea2d0a1b..d7d4fb403f6f 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1206,18 +1206,24 @@ static void init_task_vars(int idx)
        read_unlock(&tasklist_lock);
 }
 
-static void ftrace_graph_enable_direct(bool enable_branch)
+static void ftrace_graph_enable_direct(bool enable_branch, struct fgraph_ops 
*gops)
 {
        trace_func_graph_ent_t func = NULL;
        trace_func_graph_ret_t retfunc = NULL;
        int i;
 
-       for_each_set_bit(i, &fgraph_array_bitmask,
-                        sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
-               func = fgraph_array[i]->entryfunc;
-               retfunc = fgraph_array[i]->retfunc;
-               fgraph_direct_gops = fgraph_array[i];
-        }
+       if (gops) {
+               func = gops->entryfunc;
+               retfunc = gops->retfunc;
+               fgraph_direct_gops = gops;
+       } else {
+               for_each_set_bit(i, &fgraph_array_bitmask,
+                                sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
+                       func = fgraph_array[i]->entryfunc;
+                       retfunc = fgraph_array[i]->retfunc;
+                       fgraph_direct_gops = fgraph_array[i];
+               }
+       }
        if (WARN_ON_ONCE(!func))
                return;
 
@@ -1256,8 +1262,6 @@ int register_ftrace_graph(struct fgraph_ops *gops)
                ret = -ENOSPC;
                goto out;
        }
-
-       fgraph_array[i] = gops;
        gops->idx = i;
 
        ftrace_graph_active++;
@@ -1266,7 +1270,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
                ftrace_graph_disable_direct(true);
 
        if (ftrace_graph_active == 1) {
-               ftrace_graph_enable_direct(false);
+               ftrace_graph_enable_direct(false, gops);
                register_pm_notifier(&ftrace_suspend_notifier);
                ret = start_graph_tracing();
                if (ret)
@@ -1281,14 +1285,15 @@ int register_ftrace_graph(struct fgraph_ops *gops)
        } else {
                init_task_vars(gops->idx);
        }
-
        /* Always save the function, and reset at unregistering */
        gops->saved_func = gops->entryfunc;
 
        ret = ftrace_startup_subops(&graph_ops, &gops->ops, command);
+       if (!ret)
+               fgraph_array[i] = gops;
+
 error:
        if (ret) {
-               fgraph_array[i] = &fgraph_stub;
                ftrace_graph_active--;
                gops->saved_func = NULL;
                fgraph_lru_release_index(i);
@@ -1324,7 +1329,7 @@ void unregister_ftrace_graph(struct fgraph_ops *gops)
        ftrace_shutdown_subops(&graph_ops, &gops->ops, command);
 
        if (ftrace_graph_active == 1)
-               ftrace_graph_enable_direct(true);
+               ftrace_graph_enable_direct(true, NULL);
        else if (!ftrace_graph_active)
                ftrace_graph_disable_direct(false);