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

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Message-ID: <20110730163204.GH7361@thunk.org>
Date:	Sat, 30 Jul 2011 12:32:04 -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 Thu, Jul 28, 2011 at 02:11:29AM +0100, Al Viro wrote:
> Once d_move() has happened, there's nothing to protect the old parent
> anymore...  Granted, it's a hell of a narrow race window, but you
> need at least ->d_lock on your dentry...

Right, got it.  So the following should be safe according to the
dcache locking protocols, right?

	while (ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
		ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
		dentry = NULL;
		spin_lock(&inode->i_lock);
		if (!list_empty(&inode->i_dentry)) {
			dentry = list_first_entry(&inode->i_dentry,
						  struct dentry, d_alias);
			dget(dentry);
		}
		spin_unlock(&inode->i_lock);
		if (!dentry)
			break;
		next = igrab(dentry->d_parent->d_inode);
		dput(dentry);
		if (!next)
			break;
		iput(inode);
		inode = next;
		...

Let me know if I've missed anything....

						- Ted
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