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Commit 8a56d776 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Steven Rostedt
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ftrace: Fix function graph with loading of modules 



Commit 8c4f3c3f "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: default avatarDave Wysochanski <dwysocha@redhat.com>
Fixes: ed926f9b ("ftrace: Use counters to enable functions to trace")
Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 4e58e547

kernel/trace/ftrace.c

+35 −29
Original line number Diff line number Diff line
@@ -367,9 +367,6 @@ static int remove_ftrace_list_ops(struct ftrace_ops **list, 


static int __register_ftrace_function(struct ftrace_ops *ops)

{

	if (unlikely(ftrace_disabled))

		return -ENODEV;



	if (FTRACE_WARN_ON(ops == &global_ops))

		return -EINVAL;
@@ -428,9 +425,6 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops) 
{

	int ret;



	if (ftrace_disabled)

		return -ENODEV;



	if (WARN_ON(!(ops->flags & FTRACE_OPS_FL_ENABLED)))

		return -EBUSY;
@@ -2088,10 +2082,15 @@ static void ftrace_startup_enable(int command) 
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;
@@ -2113,12 +2112,17 @@ static int ftrace_startup(struct ftrace_ops *ops, int command) 
	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--;

	/*
@@ -2153,9 +2157,10 @@ static void ftrace_shutdown(struct ftrace_ops *ops, int command) 
	}



	if (!command || !ftrace_enabled)

		return;

		return 0;



	ftrace_run_update_code(command);

	return 0;

}



static void ftrace_startup_sysctl(void)
@@ -3060,8 +3065,6 @@ static void __enable_ftrace_function_probe(void) 
	if (i == FTRACE_FUNC_HASHSIZE)

		return;



	ret = __register_ftrace_function(&trace_probe_ops);

	if (!ret)

	ret = ftrace_startup(&trace_probe_ops, 0);



	ftrace_probe_registered = 1;
@@ -3069,7 +3072,6 @@ static void __enable_ftrace_function_probe(void) 


static void __disable_ftrace_function_probe(void)

{

	int ret;

	int i;



	if (!ftrace_probe_registered)
@@ -3082,8 +3084,6 @@ static void __disable_ftrace_function_probe(void) 
	}



	/* no more funcs left */

	ret = __unregister_ftrace_function(&trace_probe_ops);

	if (!ret)

	ftrace_shutdown(&trace_probe_ops, 0);



	ftrace_probe_registered = 0;
@@ -4368,10 +4368,13 @@ 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)					\

	({								\

		int ___ret = __register_ftrace_function(ops);		\

		if (!___ret)						\

			(ops)->flags |= FTRACE_OPS_FL_ENABLED;		\

		0;					\

		___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)
@@ -4780,8 +4783,6 @@ int register_ftrace_function(struct ftrace_ops *ops) 


	mutex_lock(&ftrace_lock);



	ret = __register_ftrace_function(ops);

	if (!ret)

	ret = ftrace_startup(ops, 0);



	mutex_unlock(&ftrace_lock);
@@ -4801,9 +4802,7 @@ int unregister_ftrace_function(struct ftrace_ops *ops) 
	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;
@@ -4997,6 +4996,13 @@ ftrace_suspend_notifier_call(struct notifier_block *bl, unsigned long state, 
	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_STUB | FTRACE_OPS_FL_GLOBAL |

				FTRACE_OPS_FL_RECURSION_SAFE,

};



int register_ftrace_graph(trace_func_graph_ret_t retfunc,

			trace_func_graph_ent_t entryfunc)

{
@@ -5023,7 +5029,7 @@ int register_ftrace_graph(trace_func_graph_ret_t retfunc, 
	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);
@@ -5040,7 +5046,7 @@ 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);