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

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Date:	Wed, 23 Jun 2010 10:37:58 +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).
> 
> Or it may be better to extract the body of iterate_mounts() and create a
> new function __iterate_mounts() such like that.
> 
> __iterate_mounts()
> {
> 	/* equiv to the current iterate_mounts */
> }
> 
> iterate_mount()
> {
> 	down_read(namespace_sem);
> 	or spin_lock(&vfsmount_lock);
> 
> 	__iterate_mount();
> 
> 	spin_unlock(&vfsmount_lock);
> 	or up_read(namespace_sem);
> }

Yep, thought so.
That's a useful enough function to warrant that IMHO.
I'll continue checking its usages before I do it though.

Ian


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