linux-kernel - Re: PATCH? debugfs_remove_recursive() must not rely on list_empty(d

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Message-ID: <20130725200423.GA22274@redhat.com>
Date:	Thu, 25 Jul 2013 22:04:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Alexander Z Lam <azl@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Sharp <dhsharp@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: PATCH? debugfs_remove_recursive() must not rely on
	list_empty(d_subdirs)

On 07/25, Oleg Nesterov wrote:
>
> To simplify the review, this is how it looks with the patch applied:

v2. We can use simply use list_for_each_entry_safe() and
list_next_entry() should be calles under ->i_mutex. Although
debugfs_remove_recursive() can race with itself anyway, but
still.

And the code looks much simpler. But I do not know what did
I miss.

Oleg.

void debugfs_remove_recursive(struct dentry *dentry)
{
	struct dentry *child, *next, *parent;

	if (IS_ERR_OR_NULL(dentry))
		return;

	parent = dentry->d_parent;
	if (!parent || !parent->d_inode)
		return;

	parent = dentry;
 down:
	mutex_lock(&parent->d_inode->i_mutex);
	list_for_each_entry_safe(child, next, &parent->d_subdirs, d_u.d_child) {
		if (!debugfs_positive(child))
			continue;

		/* XXX: simple_empty(child) instead ? */
		if (!list_empty(&child->d_subdirs)) {
			mutex_unlock(&parent->d_inode->i_mutex);
			parent = child;
			goto down;
		}
 up:
		__debugfs_remove(child, parent);
	}

	mutex_unlock(&parent->d_inode->i_mutex);
	if (parent != dentry) {
		child = parent;
		parent = parent->d_parent;
		mutex_lock(&parent->d_inode->i_mutex);
		next = list_next_entry(child, d_u.d_child);
		goto up;
	}

	parent = dentry->d_parent;
	mutex_lock(&parent->d_inode->i_mutex);
	__debugfs_remove(dentry, parent);
	mutex_unlock(&parent->d_inode->i_mutex);
	simple_release_fs(&debugfs_mount, &debugfs_mount_count);
}

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