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Re: [dm-devel] [PATCH v2] dm mpath: maintain reference count for underlying devices

Hi Mike,

On 09/16/11 22:59, Mike Snitzer wrote:
> When processing a request, DM-mpath's map_io() set the cloned request's
> request_queue to the appropriate underlying device's request_queue
> without getting a reference on that request_queue.
> DM-mpath now maintains a reference count on the underlying devices'
> request_queue.  This change wasn't motivated by a specific report but
> code, like blk_insert_cloned_request(), will access the request_queue
> with the understanding that the request_queue is valid.

Umm, I think it doesn't make sense.

DM opens underlying devices and it should be sufficient to keep
request_queue from being freed.
If it was not enough, any other openers would have to get the reference
count, too, and that should be done in more generic place.

Jun'ichi Nomura, NEC Corporation

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