linux-kernel - Re: debugfs_remove_recursive() while a file is in use by userspace

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Date:	Mon, 28 Dec 2015 21:42:49 +0100
From:	Nicolai Stange <nicstange@...il.com>
To:	Rajat Jain <rajatxjain@...il.com>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-newbie@...r.kernel.org, Greg Kroah-Hartman <greg@...ah.com>
Subject: Re: debugfs_remove_recursive() while a file is in use by userspace

Hi Rajat,

Rajat Jain <rajatxjain@...il.com> writes:

> Hi,
>
> I wanted to understand the behavior taken when a module calls
> debugfs_remove_recursive() on a directory, while files under that
> directory may still be in use by the userspace (for instance an
> ongoing read / write operation).
>
> Does the function wait
>
> (1) until all the currently executing file operation methods
> (read/write/map etc) have returned?
> OR
> (2) until the user has given up all references (descriptors) to the
> files under the directory (i.e. until release() method has been
> called)?

The current state is that both question are to be answered with "no",
i.e. debugfs file removal is racy.

I've recently sent a patch addressing this issue:
  https://lkml.kernel.org/g/87y4dfukzy.fsf@gmail.com

Basically, it turns the answer to your first question into "yes".
Subsequent reads/writes will return a -EIO.

That patch (series) is still under review though.

Further reference can be found in the *sub*-thread rooted at
  http://thread.gmane.org/gmane.linux.kernel/1452470/focus=1467314

Best,

Nicolai
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