[PATCH 3.2 184/185] ftrace: Fix function graph with loading of modules

Ben Hutchings
2013-12-29T02:47:36Z

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

commit 8a56d7761d2d041ae5e8215d20b4167d8aa93f51 upstream.

Commit 8c4f3c3fa9681 "ftrace: Check module functions being traced on reload"
fixed module loading and unloading with respect to function tracing, but
it missed the function graph tracer. If you perform the following

# cd /sys/kernel/debug/tracing
# echo function_graph > current_tracer
# modprobe nfsd
# echo nop > current_tracer

You'll get the following oops message:

------------[ cut here ]------------
WARNING: CPU: 2 PID: 2910 at /linux.git/kernel/trace/ftrace.c:1640 __ftrace_hash_rec_update.part.35+0x168/0x1b9()
Modules linked in: nfsd exportfs nfs_acl lockd ipt_MASQUERADE sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables uinput snd_hda_codec_idt
CPU: 2 PID: 2910 Comm: bash Not tainted 3.13.0-rc1-test #7
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
0000000000000668 ffff8800787efcf8 ffffffff814fe193 ffff88007d500000
0000000000000000 ffff8800787efd38 ffffffff8103b80a 0000000000000668
ffffffff810b2b9a ffffffff81a48370 0000000000000001 ffff880037aea000
Call Trace:
[<ffffffff814fe193>] dump_stack+0x4f/0x7c
[<ffffffff8103b80a>] warn_slowpath_common+0x81/0x9b
[<ffffffff810b2b9a>] ? __ftrace_hash_rec_update.part.35+0x168/0x1b9
[<ffffffff8103b83e>] warn_slowpath_null+0x1a/0x1c
[<ffffffff810b2b9a>] __ftrace_hash_rec_update.part.35+0x168/0x1b9
[<ffffffff81502f89>] ? __mutex_lock_slowpath+0x364/0x364
[<ffffffff810b2cc2>] ftrace_shutdown+0xd7/0x12b
[<ffffffff810b47f0>] unregister_ftrace_graph+0x49/0x78
[<ffffffff810c4b30>] graph_trace_reset+0xe/0x10
[<ffffffff810bf393>] tracing_set_tracer+0xa7/0x26a
[<ffffffff810bf5e1>] tracing_set_trace_write+0x8b/0xbd
[<ffffffff810c501c>] ? ftrace_return_to_handler+0xb2/0xde
[<ffffffff811240a8>] ? __sb_end_write+0x5e/0x5e
[<ffffffff81122aed>] vfs_write+0xab/0xf6
[<ffffffff8150a185>] ftrace_graph_caller+0x85/0x85
[<ffffffff81122dbd>] SyS_write+0x59/0x82
[<ffffffff8150a185>] ftrace_graph_caller+0x85/0x85
[<ffffffff8150a2d2>] system_call_fastpath+0x16/0x1b
---[ end trace 940358030751eafb ]---

The above mentioned commit didn't go far enough. Well, it covered the
function tracer by adding checks in __register_ftrace_function(). The
problem is that the function graph tracer circumvents that (for a slight
efficiency gain when function graph trace is running with a function
tracer. The gain was not worth this).

The problem came with ftrace_startup() which should always be called after
__register_ftrace_function(), if you want this bug to be completely fixed.

Anyway, this solution moves __register_ftrace_function() inside of
ftrace_startup() and removes the need to call them both.

Reported-by: Dave Wysochanski <dwysocha@redhat.com>
Fixes: ed926f9b35cd ("ftrace: Use counters to enable functions to trace")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
kernel/trace/ftrace.c | 68 +++++++++++++++++++++++++--------------------------
1 file changed, 34 insertions(+), 34 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -259,9 +259,6 @@ static int remove_ftrace_ops(struct ftra

static int __register_ftrace_function(struct ftrace_ops *ops)
{
- if (ftrace_disabled)
- return -ENODEV;
-
if (FTRACE_WARN_ON(ops == &global_ops))
return -EINVAL;

@@ -290,9 +287,6 @@ static int __unregister_ftrace_function(
{
int ret;

- if (ftrace_disabled)
- return -ENODEV;
-
if (WARN_ON(!(ops->flags & FTRACE_OPS_FL_ENABLED)))
return -EBUSY;

@@ -1703,10 +1697,15 @@ static void ftrace_startup_enable(int co
static int ftrace_startup(struct ftrace_ops *ops, int command)
{
bool hash_enable = true;
+ int ret;

if (unlikely(ftrace_disabled))
return -ENODEV;

+ ret = __register_ftrace_function(ops);
+ if (ret)
+ return ret;
+
ftrace_start_up++;
command |= FTRACE_UPDATE_CALLS;

@@ -1728,12 +1727,17 @@ static int ftrace_startup(struct ftrace_
return 0;
}

-static void ftrace_shutdown(struct ftrace_ops *ops, int command)
+static int ftrace_shutdown(struct ftrace_ops *ops, int command)
{
bool hash_disable = true;
+ int ret;

if (unlikely(ftrace_disabled))
- return;
+ return -ENODEV;
+
+ ret = __unregister_ftrace_function(ops);
+ if (ret)
+ return ret;

ftrace_start_up--;
/*
@@ -1768,9 +1772,10 @@ static void ftrace_shutdown(struct ftrac
}

if (!command || !ftrace_enabled)
- return;
+ return 0;

ftrace_run_update_code(command);
+ return 0;
}

static void ftrace_startup_sysctl(void)
@@ -2622,16 +2627,13 @@ static void __enable_ftrace_function_pro
if (i == FTRACE_FUNC_HASHSIZE)
return;

- ret = __register_ftrace_function(&trace_probe_ops);
- if (!ret)
- ret = ftrace_startup(&trace_probe_ops, 0);
+ ret = ftrace_startup(&trace_probe_ops, 0);

ftrace_probe_registered = 1;
}

static void __disable_ftrace_function_probe(void)
{
- int ret;
int i;

if (!ftrace_probe_registered)
@@ -2644,9 +2646,7 @@ static void __disable_ftrace_function_pr
}

/* no more funcs left */
- ret = __unregister_ftrace_function(&trace_probe_ops);
- if (!ret)
- ftrace_shutdown(&trace_probe_ops, 0);
+ ftrace_shutdown(&trace_probe_ops, 0);

ftrace_probe_registered = 0;
}
@@ -3619,12 +3619,15 @@ device_initcall(ftrace_nodyn_init);
static inline int ftrace_init_dyn_debugfs(struct dentry *d_tracer) { return 0; }
static inline void ftrace_startup_enable(int command) { }
/* Keep as macros so we do not need to define the commands */
-# define ftrace_startup(ops, command) \
- ({ \
- (ops)->flags |= FTRACE_OPS_FL_ENABLED; \
- 0; \
+# define ftrace_startup(ops, command) \
+ ({ \
+ int ___ret = __register_ftrace_function(ops); \
+ if (!___ret) \
+ (ops)->flags |= FTRACE_OPS_FL_ENABLED; \
+ ___ret; \
})
-# define ftrace_shutdown(ops, command) do { } while (0)
+# define ftrace_shutdown(ops, command) __unregister_ftrace_function(ops)
+
# define ftrace_startup_sysctl() do { } while (0)
# define ftrace_shutdown_sysctl() do { } while (0)

@@ -3964,15 +3967,8 @@ int register_ftrace_function(struct ftra

mutex_lock(&ftrace_lock);

- if (unlikely(ftrace_disabled))
- goto out_unlock;
-
- ret = __register_ftrace_function(ops);
- if (!ret)
- ret = ftrace_startup(ops, 0);
+ ret = ftrace_startup(ops, 0);

-
- out_unlock:
mutex_unlock(&ftrace_lock);
return ret;
}
@@ -3989,9 +3985,7 @@ int unregister_ftrace_function(struct ft
int ret;

mutex_lock(&ftrace_lock);
- ret = __unregister_ftrace_function(ops);
- if (!ret)
- ftrace_shutdown(ops, 0);
+ ret = ftrace_shutdown(ops, 0);
mutex_unlock(&ftrace_lock);

return ret;
@@ -4185,6 +4179,12 @@ ftrace_suspend_notifier_call(struct noti
return NOTIFY_DONE;
}

+/* Just a place holder for function graph */
+static struct ftrace_ops fgraph_ops __read_mostly = {
+ .func = ftrace_stub,
+ .flags = FTRACE_OPS_FL_GLOBAL,
+};
+
int register_ftrace_graph(trace_func_graph_ret_t retfunc,
trace_func_graph_ent_t entryfunc)
{
@@ -4211,7 +4211,7 @@ int register_ftrace_graph(trace_func_gra
ftrace_graph_return = retfunc;
ftrace_graph_entry = entryfunc;

- ret = ftrace_startup(&global_ops, FTRACE_START_FUNC_RET);
+ ret = ftrace_startup(&fgraph_ops, FTRACE_START_FUNC_RET);

out:
mutex_unlock(&ftrace_lock);
@@ -4228,7 +4228,7 @@ void unregister_ftrace_graph(void)
ftrace_graph_active--;
ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
ftrace_graph_entry = ftrace_graph_entry_stub;
- ftrace_shutdown(&global_ops, FTRACE_STOP_FUNC_RET);
+ ftrace_shutdown(&fgraph_ops, FTRACE_STOP_FUNC_RET);
unregister_pm_notifier(&ftrace_suspend_notifier);
unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);