linux-kernel - Re: OOPS in configfs when doing d

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Date:	Mon, 21 Feb 2011 02:44:01 -0800
From:	Joel Becker <jlbec@...lplan.org>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	npiggin@...nel.dk, Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: OOPS in configfs when doing d_delete

On Mon, Feb 21, 2011 at 11:20:18AM +0100, Jiri Slaby wrote:
> when configfs_attach_group fails in configfs_register_subsystem:
>         dentry = d_alloc(configfs_sb->s_root, &name);
>         if (dentry) {
>                 d_add(dentry, NULL);
> 
>                 err = configfs_attach_group(sd->s_element, &group->cg_item,
>                                             dentry);
>                 if (err) {
>                         d_delete(dentry);
>                         dput(dentry);
> 
> 
> d_delete kills the kernel. I don't know what the actual bug is here, but
> d_delete looks broken anyway:
>         spin_lock(&dentry->d_lock);
>         inode = dentry->d_inode;
>         isdir = S_ISDIR(inode->i_mode);  <======== dereference
>         if (dentry->d_count == 1) {
>                 if (inode && !spin_trylock(&inode->i_lock)) {
>                     ^^^^^  <============= test
> 
> It seems like a superfluous test, not a potential null dereference to
> me, right?

	I think you're right about the superfluous test, but I need more
investigation to see what's going on.  Thanks for the report.
	What was causing attach_group() to fail?  Do you know?

Joel

-- 

Life's Little Instruction Book #444

	"Never underestimate the power of a kind word or deed."

			http://www.jlbec.org/
			jlbec@...lplan.org
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