linux-kernel - Re: [RFC][PATCH 2/3] vfs: Add a function to lazily unmount all mounts from any dentry.

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Message-ID: <87fvsby03u.fsf@tw-ebiederman.twitter.com>
Date:	Tue, 08 Oct 2013 13:32:53 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Rob Landley <rob@...dley.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH 2/3] vfs: Add a function to lazily unmount all mounts from any dentry.

Miklos Szeredi <miklos@...redi.hu> writes:

> On Fri, Oct 04, 2013 at 03:43:18PM -0700, Eric W. Biederman wrote:
>> 
>> +void detach_mounts(struct dentry *dentry)
>> +{
>> +	struct mount *mnt, *next;
>> +	struct mountpoint *mp;
>> +
>> +	namespace_lock();
>> +	if (!d_mountpoint(dentry)) {
>> +		namespace_unlock();
>> +		return;
>> +	}
>> +	mp = new_mountpoint(dentry);
>> +	if (IS_ERR(mp)) {
>> +		return;
>> +	}
>> +	br_write_lock(&vfsmount_lock);
>> +	list_for_each_entry_safe(mnt, next, &mp->m_list, mnt_mp_list) {
>
> I don't think list_for_each_entry_safe is actually safe enough here.  Because
> propageted umounts will likely remove other mounts from the same mountpoint as
> well.  Doing it with "while (!list_empty(&mp->m_list))" should be better, and
> AFAICS it will always make progress.

Thanks I will take a look.  But on the surface that logic sounds
correct.

Eric
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