Re: [RFC PATCH 3/3] blk-mq: Remove generation seqeunce

[Keith Busch <keith.busch@linux.intel.com>]

On Tue, May 22, 2018 at 11:07:07PM +0800, Ming Lei wrote:
> > At approximately the same time, you're saying the driver that returned
> > EH_HANDLED may then call blk_mq_complete_request() in reference to the
> > *old* request that it returned EH_HANDLED for, incorrectly completing
> 
> Because this request has been completed above by blk-mq timeout,
> then this old request won't be completed any more via blk_mq_complete_request()
> either from normal path or what ever, such as cancel.
 
> > the new request before it is done. That will inevitably lead to data
> > corruption. Is that happening today in any driver?
> 
> No such issue since current blk-mq makes sure one req is only completed
> once, but your patch changes to depend on driver to make sure that.

The blk-mq timeout complete makes the request available for allocation
as a new command, at which point blk_mq_complete_request can be called
again. If a driver is somehow relying on blk-mq to prevent a double
completion for a previously completed request context, they're already
in a lot of trouble.