linux-kernel - Re: [autofs] [PATCH 04/38] autofs4: Save autofs trigger's vfsmount in super block info

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Date:	Thu, 24 Jun 2010 09:35:50 +0800
From:	Ian Kent <raven@...maw.net>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	Miklos Szeredi <miklos@...redi.hu>, viro@...iv.linux.org.uk,
	vaurora@...hat.com, autofs@...ux.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, jblunck@...e.de
Subject: Re: [autofs] [PATCH 04/38] autofs4: Save autofs trigger's vfsmount
 in super block info

On Wed, 2010-06-23 at 11:07 +0900, J. R. Okajima wrote:
> Ian Kent:
> > I may be missing something about this, but why is it safe to use
> > iterate_mounts(), since it doesn't take the vfsmount_lock when
> > traversing the list of mounts?
> 
> The sample code was not correct.
> We need to acquire vfsmount_lock or down_read(namespace_sem).

This is looking more and more suspect the more I dig.

The only place iterate_mounts() is called is within the audit subsystem
AFAICS, and I don't see where vfsmount_lock is taken in that code. OTOH,
in fs/namespace.c it is pretty clear that vfsmount->mnt_list is
protected by the vfsmount_lock.

Ummm ... that's gota be broken but maybe someone can give a reason why
it isn't?

Ian


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