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

Keith Busch
2018-05-22T15:01:19Z

On Tue, May 22, 2018 at 10:57:40PM +0800, Ming Lei wrote:
> OK, that still depends on driver's behaviour, even though it is true
> for NVMe, you still have to audit other drivers about this sync
> because it is required by your patch.

Okay, forget about nvme for a moment here. Please run this thought
experiment to decide if what you're saying is even plausible for any
block driver with the existing implementation:

Your scenario has a driver return EH_HANDLED for a timed out request. The
timeout work then completes the request. The request may then be
reallocated for a new command and dispatched.

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
the new request before it is done. That will inevitably lead to data
corruption. Is that happening today in any driver?