Re: [REGRESSION v4.10-rc1] blkdev_issue_zeroout() returns -EREMOTEIO on the first call for SCSI device that doesn't support WRITE SAME

[Jens Axboe <axboe@kernel.dk>]

On 02/03/2017 09:12 AM, Christoph Hellwig wrote:
> On Fri, Feb 03, 2017 at 08:21:31AM -0700, Jens Axboe wrote:
>>> Error 121 (EREMOTEIO) was returned from blkdev_issue_zeroout().
>>> That came from sd driver because WRITE SAME was sent to the device
>>> which didn't support it.
>>>
>>> The problem was introduced by commit e73c23ff736e ("block: add async
>>> variant of blkdev_issue_zeroout"). Before the commit, blkdev_issue_zeroout
>>> fell back to normal zero writing when WRITE SAME failed and it seems
>>> sd driver's heuristics depends on that behaviour.
>>
>> CC Christoph and Chaitanya.
> 
> And adding Martin as the sd.c Write Same code is his.
> 
> I suspect we'll have to restore the old way this works for 4.10 as it's
> too late in the cycle, but that whole idea of trying Write Same first
> and just disabling it if it doesn't work is a receipe for desaster -
> it kinda works for a synchronous blkdev_issue_zeroout, but if we want
> to be able to submit it asynchronously it's getting too hairy to handle.

I agree, the current approach is a hot and ugly mess.

> I think we should fix sd.c to only send WRITE SAME if either of the
> variants are explicitly listed as supported through
> REPORT SUPPORTED OPERATION CODES, or maybe through a whitelist if
> there are important enough devices.

Yep

-- 
Jens Axboe