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Subject: Re: [PATCH tracing/kprobes 2/6] ftrace: Fix trace_add_event_call()
 to initialize list
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       lkml <linux-kernel@vger.kernel.org>,
       systemtap <systemtap@sources.redhat.com>,
       DLE <dle-develop@lists.sourceforge.net>,
       Jim Keniston <jkenisto@us.ibm.com>,
       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
       Andi Kleen <ak@linux.intel.com>, Christoph Hellwig <hch@infradead.org>,
       "Frank Ch. Eigler" <fche@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
       Jason Baron <jbaron@redhat.com>, "K.Prasad" <prasad@linux.vnet.ibm.com>,
       Lai Jiangshan <laijs@cn.fujitsu.com>, Li Zefan <lizf@cn.fujitsu.com>,
       Peter Zijlstra <peterz@infradead.org>,
       Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
       Tom Zanussi <tzanussi@gmail.com>
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Organization: Kihon Technologies Inc.
Date: Tue, 15 Sep 2009 19:51:21 -0400
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On Mon, 2009-09-14 at 16:49 -0400, Masami Hiramatsu wrote:
> Initialize event_call.list and 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 |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> 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.


>  	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);

But this I can see is needed ;-)

-- Steve

> +	return ret;
>  }
>  
>  /* Add an additional event_call dynamically */
> 
> 

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