blk-mq: fix racy updates of rq->errors

[Christoph Hellwig]

On Tue, Oct 06, 2015 at 09:54:42PM +0300, Dan Carpenter wrote:
>    622                  if (req->cmd_type == REQ_TYPE_DRV_PRIV) {
>    623                          if (cmd_rq->ctx == CMD_CTX_CANCELLED)
>    624                                  status = -EINTR;
> 
> This looks like it's supposed to be a bitmap.

It's not - it's a value that can have either positive (nvme status codes)
or negative Linux errnos.  It really should be an int just like req->errors
was before.  I'll send a patch to Jens.

Signed-off-by: Christoph Hellwig <hch at lst.de>