linux-kernel - Re: [PATCH 1/2] Disk hot removal causing oopses and fixes

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Message-ID: <4AF089C1.4010806@s5r6.in-berlin.de>
Date:	Tue, 03 Nov 2009 20:51:29 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Jarkko Lavinen <jarkko.lavinen@...ia.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH 1/2] Disk hot removal causing oopses and fixes

Jarkko Lavinen wrote:
> Hi Steven
> 
> Sorry for late reply.
> 
>> It has to reference-count its objects so that they are not freed as long
>> as they are used by upper layers,
> 
> The block layer and device removal seems to be designed from
> top-down approach.  Althouh disc is referenced from
> __blkdev_get(), disc's request queue is not.  Also
> blk_cleanup_queue() calls elevator_exit() without caring if
> anyone still uses the elevator.
[...]

I still don't understand how there can be a problem here.  Shouldn't the
sequence be:

 1. low-level determines that a device went away
 2. low-level takes note that from now on no new requests must be
    enqueued anymore
 3. low-level calls blk_cleanup_queue
 4. blk_cleanup_queue waits until remaining requests are done
    (it calls blk_sync_queue)
 5. blk_cleanup_queue cleans up block layer data
 6. low-level can now clean up/ free its own data

Does the MMC layer miss step 2?  Because without this, step 4 would be
in vain.
-- 
Stefan Richter
-=====-==--= =-== ---==
http://arcgraph.de/sr/
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