linux-kernel - Re: [PATCH] Revert "debugfs: ->d_parent is never NULL or negative"

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Message-ID: <20161006224117.GP19539@ZenIV.linux.org.uk>
Date:   Thu, 6 Oct 2016 23:41:17 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     timur@...eaurora.org, cov@...eaurora.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "debugfs: ->d_parent is never NULL or negative"

On Thu, Oct 06, 2016 at 11:37:29PM +0100, Al Viro wrote:

> If you ever get NULL in ->d_parent of struct dentry instance, you are
> practically certain to have a dangling pointer to memory that used to
> contain a struct dentry at some point but got freed and reused since then.

... which is what happens in your case, apparently.  ->stats is still
pointing to a dentry that had just been freed and its memory reused.