On 29/11/16 12:28, David Vrabel wrote: > On 29/11/16 11:19, Juergen Gross wrote: >> On 29/11/16 12:14, Jan Beulich wrote: >>>>>> On 29.11.16 at 11:50, <[email protected]> wrote: >>>> --- a/drivers/scsi/xen-scsifront.c >>>> +++ b/drivers/scsi/xen-scsifront.c >>>> @@ -184,8 +184,6 @@ static struct vscsiif_request >>>> *scsifront_pre_req(struct vscsifrnt_info *info) >>>> >>>> ring_req = RING_GET_REQUEST(&(info->ring), ring->req_prod_pvt); >>>> >>>> - ring->req_prod_pvt++; >>> >>> Please note the "_pvt" suffix, which stands for "private": This field is >>> not visible to the backend. Only ring->sring fields are shared, and >>> the updating of the shared field happens in RING_PUSH_REQUESTS() >>> and RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(). >> >> Sure, but RING_PUSH_REQUESTS() will copy req_prod_pvt to req_prod. In >> the case corrected this would advance req_prod by two after the error >> case before, even if only one request would have made it to the ring. >> >> As an alternative I could have decremented req_prod_pvt in case of an >> error, but I like my current solution better. > > FWIW, I found the commit message a bit misleading and also came to the > same conclusion as Jan initially. > > Perhaps, > > "When adding a new request to the ring, an error may cause the > (partially constructed) request to be discarded and used for the next. > Thus ring->req_prod_pvt should not be advanced until we know the request > will be successfully added to the ring."
This is indeed much better, thanks. In case there are no other objections I'll fix this up when committing. Juergen
