linux-kernel - loop: busywait for release?

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Date:	Fri, 21 Jan 2011 01:31:45 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
cc:	Jens Axboe <jaxboe@...ionio.com>, Christoph Hellwig <hch@....de>
Subject: loop: busywait for release?

to the principal editors of drivers/block/loop.c,

Hi,

I have here a program that sets up a loop device, does its
(quite minimal) work and releases the loop device again.

As soon as a loop device is set up using LOOP_SET_FD, userspace
programs like udev immediately pounce on the loop device for fstype
identification and whatnot, and render the release of the device
futile with -EBUSY.

I could retry until EBUSY is no longer returned, however, since I see
nothing in the loop device driver that could help fence off _new
openers_, EBUSY may be encountered indefinitely.

I reckon vfsmounts have the same issue, though one can use `umount -l` 
to fence new processes off, and then (if desired) kill existing ones.

What is the preferred way to solve this for loop?

thanks,
Jan
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