From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: [RFC][PATCH 1/3] vfs: Keep a list of mounts on a mount point
Date: Tue, 08 Oct 2013 13:31:45 -0700
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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>
To: Miklos Szeredi <miklos@szeredi.hu>
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In-Reply-To: <20131008134453.GG14242@tucsk.piliscsaba.szeredi.hu> (Miklos
	Szeredi's message of "Tue, 8 Oct 2013 15:44:53 +0200")
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Miklos Szeredi <miklos@szeredi.hu> writes:

>> @@ -691,6 +693,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
>>  	list_del_init(&mnt->mnt_hash);
>>  	put_mountpoint(mnt->mnt_mp);
>>  	mnt->mnt_mp = NULL;
>> +	list_del_init(&mnt->mnt_mp_list);
>
> Should be done *before* put_mountpoint(), for obvious reasons.
>
> And a BUG_ON(!list_empty(&mp->m_list)) in put_mountpoint() for good measure (and
> no, WARN_ON() is not better here, since use-after-free is definitely worse than
> a BUG).

Good point.  I will take a look at making this change shortly and repost
the patches.


>>  }
>>  
>>  /*
>> @@ -705,6 +708,7 @@ void mnt_set_mountpoint(struct mount *mnt,
>>  	child_mnt->mnt_mountpoint = dget(mp->m_dentry);
>>  	child_mnt->mnt_parent = mnt;
>>  	child_mnt->mnt_mp = mp;
>> +	list_add_tail(&child_mnt->mnt_mp_list, &mp->m_list);
>>  }
>>  
>>  /*
>> @@ -1193,6 +1197,7 @@ void umount_tree(struct mount *mnt, int propagate)
>>  			p->mnt_parent->mnt_ghosts++;
>>  			put_mountpoint(p->mnt_mp);
>>  			p->mnt_mp = NULL;
>> +			list_del_init(&mnt->mnt_mp_list);
>
> Ditto.
>
>>  		}
>>  		change_mnt_propagation(p, MS_PRIVATE);
>>  	}
>> -- 
>> 1.7.5.4
>>