linux-kernel - Re: [RFC][PATCH] debugfs: Fix corrupted loop in debugfs_remove

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Date:	Thu, 12 Jun 2014 09:08:27 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] debugfs: Fix corrupted loop in
 debugfs_remove_recursive

On Thu, Jun 12, 2014 at 11:43:14AM +0100, Al Viro wrote:
> On Mon, Jun 09, 2014 at 02:06:07PM -0400, Steven Rostedt wrote:
> 
> > When these are called, the d_entry and inode locks need to be released
> > to call the instance creation and deletion code. That code has its own
> > accounting and locking to serialize everything to prevent multiple
> > users from causing harm. As the parent "instance" directory can not
> > be modified this simplifies things.
> 
> Yecchhh...   Looking at debugfs:
> 
> static inline int debugfs_positive(struct dentry *dentry)
> {
>         return dentry->d_inode && !d_unhashed(dentry);
> }
> 
> ...
>         if (debugfs_positive(dentry)) {
>                 if (dentry->d_inode) {
> What the hell?
> 
>         parent = dentry->d_parent;
>         if (!parent || !parent->d_inode)
>                 return;
> Huh?  First of all, ->d_parent is *never* NULL.  Moreover, it can't be a
> negative dentry.
> 
> What's more, if debugfs_rename() is ever used for cross-directory renames,
> this tree-walker is buggered - it'll happily walk up "back" into a directory
> it has never visited...

All of that code has been there since before 2.11, I really don't
remember how I came up with it at all, sorry.

I'm working on converting debugfs to use kernfs, so all of the debugfs
mess and problems should go away soon.

thanks,

greg k-h
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