linux-kernel - Re: I_CLEAR bug while shrinking dcache

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Message-ID: <20150414124428.GW889@ZenIV.linux.org.uk>
Date:	Tue, 14 Apr 2015 13:44:29 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Samuel Thibault <samuel.thibault@...-lyon.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: I_CLEAR bug while shrinking dcache

On Tue, Apr 14, 2015 at 10:12:54AM +0200, Samuel Thibault wrote:

> So it seems that shrink_dentry_list was trying to kill an inode which
> already has I_CLEAR.  I'll be trying the attached patch in the next
> days.

That patch is just papering over the problem.  What you have is a dentry
with ->d_inode pointing to something with I_CLEAR set.

So either
	* dentry has already been through __dentry_kill()
	* or you have live dentry with ->d_inode somehow not contributing
to refcount of ->d_inode
	* or you have an inode with positive refcount and I_CLEAR set.

The first variant can happen, but in that case it should have had
DCACHE_DENTRY_KILLED set by said __dentry_kill() and skipped.  The other
two are clear inode refcounting bugs.

Do you have a reproducer for that?
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