linux-ext4 - Re: [PATCH] ext4: fix races in ext4_sync

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Date:	Wed, 27 Jul 2011 20:34:22 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: fix races in ext4_sync_parent()

On Wed, Jul 27, 2011 at 02:15:54AM +0100, Al Viro wrote:
> On Tue, Jul 26, 2011 at 09:13:12PM -0400, Theodore Ts'o wrote:
> > +	inode = igrab(inode);
> > +	while (ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
> >  		ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
> > -		dentry = list_entry(inode->i_dentry.next,
> > -				    struct dentry, d_alias);
> > -		if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode)
> > +		dentry = list_first_entry(&inode->i_dentry,
> > +					  struct dentry, d_alias);
> 
> ... and what if you don't have a dentry for that inode anymore?

I thought you were complaining that dentry could never be NULL
earlier?  We earlier checked for NULL, but I figured you knew
something I didn't....

> > +		next = igrab(dentry->d_parent->d_inode);
> 
> what protects you against rename() (OK, d_mode()) here?

Does it matter?  We'll get either the old or the new parent directory,
but either way it will be a valid inode, right?  Or am I missing
something?

						- Ted
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