Re: [PATCH] nbd: restore default timeout when setting it to zero

[Hou Pu <houpu@bytedance.com>]

On 2020/8/21 3:03 AM, Josef Bacik wrote:
> On 8/10/20 8:00 AM, Hou Pu wrote:
> > If we configured io timeout of nbd0 to 100s. Later after we
> > finished using it, we configured nbd0 again and set the io
> > timeout to 0. We expect it would timeout after 30 seconds
> > and keep retry. But in fact we could not change the timeout
> > when we set it to 0. the timeout is still the original 100s.
> >
> > So change the timeout to default 30s when we set it to zero.
> > It also behaves same as commit 2da22da57348 ("nbd: fix zero
> > cmd timeout handling v2").
> >
> > It becomes more important if we were reconfigure a nbd device
> > and the io timeout it set to zero. Because it could take 30s
> > to detect the new socket and thus io could be completed more
> > quickly compared to 100s.
> >
> > Signed-off-by: Hou Pu <houpu@bytedance.com>
> > ---
> >   drivers/block/nbd.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > index ce7e9f223b20..bc9dc1f847e1 100644
> > --- a/drivers/block/nbd.c
> > +++ b/drivers/block/nbd.c
> > @@ -1360,6 +1360,8 @@ static void nbd_set_cmd_timeout(struct 
> > nbd_device *nbd, u64 timeout)
> >       nbd->tag_set.timeout = timeout * HZ;
> >       if (timeout)
> >           blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
> > +    else
> > +        blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
> >   }
> >   /* Must be called with config_lock held */
>
> What about the tag_set.timeout?  Thanks,

I think user space could set io timeout to 0, thus we set 
tag_set.timeout = 0 here and also we should tell the block layer
to restore 30s timeout in case it is not. tag_set.timeout == 0
imply 30s io timeout and retrying after timeout.

(Sorry, I am not sure if I understand your question here. Could
you explain a little more if needed?)

Thanks,
Hou

> Josef