linux-kernel - Re: [PATCH 6/6] tracing: Change remove_event_file_dir() to clear "d_subdirs"->i

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Date:	Wed, 24 Jul 2013 16:08:00 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Alexander Z Lam <azl@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Sharp <dhsharp@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] tracing: Change remove_event_file_dir() to clear
 "d_subdirs"->i_private

On Tue, 2013-07-23 at 22:59 +0200, Oleg Nesterov wrote:
> Change remove_event_file_dir() ->i_private for every file we
> are going to remove.
> 
> tracing_open_generic_file() and tracing_release_generic_file()
> can go away, ftrace_enable_fops and ftrace_event_filter_fops()
> use tracing_open_generic() but only to check tracing_disabled.
> 
> This fixes all races with event_remove() or instance_delete().
> f_op->read/write/whatever can never use the freed file/call,
> all event/* files were changed to check and use ->i_private
> under event_mutex.
> 
> Note: this doesn't not fix other problems, event_remove() can
> destroy the active ftrace_event_call, we need more changes but
> those changes are completely orthogonal.

Hmm, but this patch opens up that race right? We remove the tr ref
counter updates here.

> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/trace_events.c |   40 ++++++++--------------------------------
>  1 files changed, 8 insertions(+), 32 deletions(-)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 3ae037c..298e4fa 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -428,42 +428,19 @@ static void *event_file_data(struct file *filp)
>  
>  static void remove_event_file_dir(struct ftrace_event_file *file)
>  {
> +	struct dentry *dir = file->dir;
> +	struct dentry *child;

Need space here.

> +	/* ->i_mutex is not needed, nodody can create/remove a file */

"nodody" ;-)

-- Steve

> +	list_for_each_entry(child, &dir->d_subdirs, d_u.d_child)
> +		child->d_inode->i_private = NULL;
> +
>  	list_del(&file->list);
> -	debugfs_remove_recursive(file->dir);
> +	debugfs_remove_recursive(dir);
>  	remove_subsystem(file->system);
>  	kmem_cache_free(file_cachep, file);
>  }
>  
>  /*
> - * Open and update trace_array ref count.
> - * Must have the current trace_array passed to it.
> - */
> -static int tracing_open_generic_file(struct inode *inode, struct file *filp)
> -{
> -	struct ftrace_event_file *file = inode->i_private;
> -	struct trace_array *tr = file->tr;
> -	int ret;
> -
> -	if (trace_array_get(tr) < 0)
> -		return -ENODEV;
> -
> -	ret = tracing_open_generic(inode, filp);
> -	if (ret < 0)
> -		trace_array_put(tr);
> -	return ret;
> -}
> -
> -static int tracing_release_generic_file(struct inode *inode, struct file *filp)
> -{
> -	struct ftrace_event_file *file = inode->i_private;
> -	struct trace_array *tr = file->tr;
> -
> -	trace_array_put(tr);
> -
> -	return 0;
> -}
> -
> -/*
>   * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
>   */
>  static int
> @@ -1274,10 +1251,9 @@ static const struct file_operations ftrace_set_event_fops = {
>  };
>  
>  static const struct file_operations ftrace_enable_fops = {
> -	.open = tracing_open_generic_file,
> +	.open = tracing_open_generic,
>  	.read = event_enable_read,
>  	.write = event_enable_write,
> -	.release = tracing_release_generic_file,
>  	.llseek = default_llseek,
>  };
>  


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