From: ebiederm@xmission.com (Eric W. Biederman)
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: "Serge E. Hallyn" <serge@hallyn.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>, Rob Landley <rob@landley.net>,
        Linus Torvalds <torvalds@linux-foundation.org>
References: <CAJfpegsxgnSRUW-E5HM3uT5QfGyUtn_v=i4Ppkkkutp34287AA@mail.gmail.com>
	<87a9kkax0j.fsf@xmission.com>
	<CAJfpeguv+7giYNpAuXE9Ja_9BEwB0-fZBVgRSeVqpzSXgQYZ6Q@mail.gmail.com>
	<8761v7h2pt.fsf@tw-ebiederman.twitter.com>
	<CAJfpegtT7y-1HhbEVAMKkdQugTG_w7G_epGtQHGvQLpcZB5FVA@mail.gmail.com>
	<87li281wx6.fsf_-_@xmission.com> <87a9io1wu1.fsf_-_@xmission.com>
	<20131008135648.GH14242@tucsk.piliscsaba.szeredi.hu>
Date: Tue, 08 Oct 2013 13:32:53 -0700
In-Reply-To: <20131008135648.GH14242@tucsk.piliscsaba.szeredi.hu> (Miklos
	Szeredi's message of "Tue, 8 Oct 2013 15:56:48 +0200")
Message-ID: <87fvsby03u.fsf@tw-ebiederman.twitter.com>
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Subject: Re: [RFC][PATCH 2/3] vfs: Add a function to lazily unmount all mounts from any dentry.
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Miklos Szeredi <miklos@szeredi.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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