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

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Message-ID: <20151228203031.GI20997@ZenIV.linux.org.uk>
Date:	Mon, 28 Dec 2015 20:30:31 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Rajat Jain <rajatxjain@...il.com>
Cc:	"linux-kernel@...r.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

On Mon, Dec 28, 2015 at 12:27:22PM -0800, Rajat Jain wrote:
> 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?

No

> 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)?

... and no.  Don't use debugfs for objects that might have a finite
lifetime, or you'll get trouble.  And don't use debugfs outside of
well-isolated testing systems.
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