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 11:07:13 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Ian Kent <raven@...maw.net>
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


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);
}


J. R. Okajima
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