[PATCH tracing/kprobes 2/6] ftrace: Fix trace_add_event_call() to initialize list take 2

[Masami Hiramatsu <mhiramat@redhat.com>]

Steven Rostedt wrote:
> On Wed, 2009-09-16 at 10:17 -0400, Masami Hiramatsu wrote:
>> Steven Rostedt wrote:
> 
>>>> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
>>>> index ba34920..38e82a5 100644
>>>> --- a/kernel/trace/trace_events.c
>>>> +++ b/kernel/trace/trace_events.c
>>>> @@ -1009,10 +1009,14 @@ static int __trace_add_event_call(struct ftrace_event_call *call)
>>>>   	if (!d_events)
>>>>   		return -ENOENT;
>>>>
>>>> +	INIT_LIST_HEAD(&call->list);
>>>
>>> The INIT_LIST_HEAD is not needed here. The list_add will assign it.
>>
>> Without initializing it, list debugging code warns always :-)
>> Please see, __list_add()@lib/list_debug.c
> 
> /me looks
> 
> from: include/linux/list.h
> 
> static inline void list_add(struct list_head *new, struct list_head *head)
> {
> 	__list_add(new, head, head->next);
> }
> 
> from: lib/list_debug.c
> 
> void __list_add(struct list_head *new,
> 			      struct list_head *prev,
> 			      struct list_head *next)
> {
> 	WARN(next->prev != prev,
> 		"list_add corruption. next->prev should be "
> 		"prev (%p), but was %p. (next=%p).\n",
> 		prev, next->prev, next);
> 	WARN(prev->next != next,
> 		"list_add corruption. prev->next should be "
> 		"next (%p), but was %p. (prev=%p).\n",
> 		next, prev->next, prev);
> 	next->prev = new;
> 	new->next = next;
> 	new->prev = prev;
> 	prev->next = new;
> }
> 
> What you pass in is:
> 
>          list_add(&call->list,&ftrace_events);
> 
> new =&call->list;
> prev =&ftrace_events->prev;
> next =&ftrace_events->next;
> 
> The above code never tests "new". The INIT_LIST_HEAD is useless.

Oh, I see, I misunderstood. Thank you for pointing it out. :)
Here, I updated the patch.

---
ftrace: Fix trace_add_event_call() to initialize list

From: Masami Hiramatsu <mhiramat@redhat.com>

Handle failuer path in trace_add_event_call() for fixing below bug
which occurred when I tried to add invalid event twice.

Could not create debugfs 'kmalloc' directory
Failed to register kprobe event: kmalloc
Faild to register probe event(-1)
------------[ cut here ]------------
WARNING: at /home/mhiramat/ksrc/random-tracing/lib/list_debug.c:26
__list_add+0x27/0x5c()
Hardware name:
list_add corruption. next->prev should be prev (c07d78cc), but was
00001000. (next=d854236c).
Modules linked in: sunrpc uinput virtio_net virtio_balloon i2c_piix4 pcspkr
i2c_core virtio_blk virtio_pci virtio_ring virtio [last unloaded:
scsi_wait_scan]
Pid: 1394, comm: tee Not tainted 2.6.31-rc9 #51
Call Trace:
 [<c0438424>] warn_slowpath_common+0x65/0x7c
 [<c05371b3>] ? __list_add+0x27/0x5c
 [<c043846f>] warn_slowpath_fmt+0x24/0x27
 [<c05371b3>] __list_add+0x27/0x5c
 [<c047f050>] list_add+0xa/0xc
 [<c047f8f5>] trace_add_event_call+0x60/0x97
 [<c0483133>] command_trace_probe+0x42c/0x51b
 [<c044a1b3>] ? remove_wait_queue+0x22/0x27
 [<c042a9c0>] ? __wake_up+0x32/0x3b
 [<c04832f6>] probes_write+0xd4/0x10a
 [<c0483222>] ? probes_write+0x0/0x10a
 [<c04b27a9>] vfs_write+0x80/0xdf
 [<c04b289c>] sys_write+0x3b/0x5d
 [<c0670d41>] syscall_call+0x7/0xb
---[ end trace 2b962b5dc1fdc07d ]---

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jason Baron <jbaron@redhat.com>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
---

 kernel/trace/trace_events.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)


diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index ba34920..83cc2c0 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1010,9 +1010,12 @@ static int __trace_add_event_call(struct ftrace_event_call *call)
 		return -ENOENT;

 	list_add(&call->list, &ftrace_events);
-	return event_create_dir(call, d_events, &ftrace_event_id_fops,
+	ret = event_create_dir(call, d_events, &ftrace_event_id_fops,
 				&ftrace_enable_fops, &ftrace_event_filter_fops,
 				&ftrace_event_format_fops);
+	if (ret < 0)
+		list_del(&call->list);
+	return ret;
 }

 /* Add an additional event_call dynamically */


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com