linux-kernel - Re: [tracepoint] cargo-culting considered harmful...

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Date:	Wed, 23 Jan 2013 18:02:35 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [tracepoint] cargo-culting considered harmful...

On Wed, Jan 23, 2013 at 10:55:24PM +0000, Al Viro wrote:
> In samples/tracepoints/tracepoint-probe-sample.c:
> /*
>  * Here the caller only guarantees locking for struct file and struct inode.
>  * Locking must therefore be done in the probe to use the dentry.
>  */
> static void probe_subsys_event(void *ignore,   
>                                struct inode *inode, struct file *file)
> {
>         path_get(&file->f_path);
>         dget(file->f_path.dentry);
>         printk(KERN_INFO "Event is encountered with filename %s\n",
>                 file->f_path.dentry->d_name.name);
>         dput(file->f_path.dentry);
>         path_put(&file->f_path);
> }
> 
> note that
> 	* file->f_path is already pinned down by open(), path_get() does not
> provide anything extra.
> 	* file->f_path.dentry is already pinned by open() *and* path_get()
> just above that dget().
> 	* ->d_name.name *IS* *NOT* *PROTECTED* by pinning dentry down,
> whether it's done once or thrice.
> 
> I do realize that it's just an example, but perhaps we should rename that
> file to match the contents?  The only question is whether it should be
> git mv samples/tracepoints/{tracepoint-probe-sample,cargo-cult}.c
> or git mv samples cargo-cult...

I wonder if we should just remove the samples/tracepoints/ all together.
The tracepoint code is now only used internally by the trace_event code,
and there should not be any users of tracepoints directly.

-- Steve

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