From owner-freebsd-hackers@FreeBSD.ORG  Tue Apr 26 10:18:30 2011
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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Tue, 26 Apr 2011 12:17:23 +0200
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Cc: Bartosz Fabianowski <freebsd@chillt.de>
Subject: Re: Is there some implicit locking of device methods?
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On Tuesday 26 April 2011 11:52:27 Bartosz Fabianowski wrote:
> 1. attach() is running and executes make_dev(). Before attach() has 
> finished, someone calls open() on the newly created device node and 
> tries to read from a device that is not fully instantiated.
> 
> 2. read() is running when the device is suddenly pulled (this is a USB 
> device) so that detach() gets run. Thus, detach() starts tearing down 
> data structures that read() may still be accessing.

Hi,

You need to handle all cases in your driver. Fortunately there exists a 
solution for this already, called USB cdev. See

serial/ulpt.c

for example.

--HPS