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

From: Stefan Richter
Date: Tue Nov 03 2009 - 14:51:42 EST

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
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