linux-kernel - Re: Reference counting of MMC host driver modules

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Message-ID: <496B7969.5050706@s5r6.in-berlin.de>
Date:	Mon, 12 Jan 2009 18:10:01 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Enrik Berkhan <Enrik.Berkhan@...com>
CC:	Pierre Ossman <drzeus-mmc@...eus.cx>,
	David Vrabel <david.vrabel@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: Reference counting of MMC host driver modules

Enrik Berkhan wrote:
> When removing the mmc_host_driver, everything seems to be fine; the
> MMC/SD block device has been deactivated by mmc_blk_remove(), that in
> turn has stopped the queue via mmc_cleanup_queue(). mmc_cleanup_queue()
> calls blk_cleanup_queue() on the underlying struct request_queue. By
> this, the reference count of the struct request_queues kboj drops to
> zero. The MD driver still has the block device open and, actually,
> things work fine unless the memory of the struct request_queue isn't
> touched, because it is marked dead. Of course, accessing the MD device
> returns EIO, but that's fine.
> 
> When the mmc_host_driver is reloaded, new struct request_queues will be
> allocated and with some probability, the old memory will be re-used for
> them or the old memory locations will be re-used for something else. The
> key point is that the queues still in use by the MD layer will
> effectively no longer be marked dead or completely corrupted.

So in short, the request_queue's reference count goes to zero even
though something still points to it?
-- 
Stefan Richter
-=====-==--= ---= -==--
http://arcgraph.de/sr/
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