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Date: Wed, 17 Dec 2008 10:16:45 -0800
From: Greg KH <greg@kroah.com>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: linux-kernel@vger.kernel.org, v4l <video4linux-list@redhat.com>,
        Laurent Pinchart <laurent.pinchart@skynet.be>
Subject: Re: [BUG] cdev_put() race condition
Message-ID: <20081217181645.GA26161@kroah.com>
References: <200812082156.26522.hverkuil@xs4all.nl> <200812170023.41936.hverkuil@xs4all.nl> <20081216233039.GA20338@kroah.com> <200812171437.33695.hverkuil@xs4all.nl>
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On Wed, Dec 17, 2008 at 02:37:33PM +0100, Hans Verkuil wrote:
> > Again, don't use cdev's reference counting for your own object
> > lifecycle, it is different and will cause problems, like you have found
> > out.
> 
> Sigh. It has nothing to do with how v4l uses it. And to demonstrate this, 
> here is how you reproduce it with the sg module (tested it with my USB 
> harddisk).
> 
> 1) apply this patch to char_dev.c:

<snip>

Ok, since I can't convince you that using a cdev for your reference
counting is incorrect, I'll have to go change the cdev code to prevent
you from doing this :(

Anyway, do you have a patch for the cdev code to propose how to fix this
issue you are having?

thanks,

greg k-h