[dpdk-stable] [PATCH v2 4/4] net/failsafe: fix removed device handling

[Gaëtan Rivet]

On Thu, Dec 14, 2017 at 10:40:22AM +0000, Matan Azrad wrote:
> Hi Gaetan
> 

<snip>

> > >
> > > If you add this check in the iterator itself, you would skip removed
> > > devices before attempting operating upon them, right?
> > >
> > > Then it should probably help with your issue, unless you tested it and
> > > verified that it didnt?
> > >
> > > Something like this:
> > >
> > > ---8<---
> > >
> > > diff --git a/drivers/net/failsafe/failsafe_private.h
> > > b/drivers/net/failsafe/failsafe_private.h
> > > index d81cc3ca6..62ddc0689 100644
> > > --- a/drivers/net/failsafe/failsafe_private.h
> > > +++ b/drivers/net/failsafe/failsafe_private.h
> > > @@ -316,8 +316,12 @@ fs_find_next(struct rte_eth_dev *dev,
> > >         subs = PRIV(dev)->subs;
> > >         tail = PRIV(dev)->subs_tail;
> > >         while (sid < tail) {
> > > +               if (min_state > DEV_PROBED &&
> > > +                   fs_is_removed(&sub[sid]))
> > > +                       goto next;
> > >                 if (subs[sid].state >= min_state)
> > >                         break;
> > > +next:
> > >                 sid++;
> > >         }
> > >         *sid_out = sid;
> > >
> > > --->8---
> > >
> > > Only issue being that it is completely racy, but as this MT-unsafe
> > > property is inescapable we might as well ignore it and go for KISS.
> > >
> > > If that's enough, I would prefer instead of having this additional
> > > check added to all rte_eth operations.
> > >
> > 
> > Ok, actually you were right here to do it this way. The "is_removed"
> > check needs to happen after the operation attempt to effectively mitigate
> > the possible race. Checking before attempting the call will be much less
> > effective.
> > 
> > That being said, would it be cleaner to have eth_dev ops return -ENODEV
> > directly, and check against it within fail-safe?
> > 
> 
> I think that according to "is_removed" semantic we must return a Boolean value (Each value different from '0' means that the device is removed) like other functions in c library (for example isspace()).
> 

Sure, I wasn't discussing the interface proposed by rte_eth_dev_is_removed().

What I meant was to ask whether checking rte_eth_dev_is_removed() would
be more interesting in the ethdev layer, making the eth_dev_ops return
-ENODEV regardless of the previous error if this check is supported by
the driver and signal that the port is removed.

I think this information could be interesting to other systems, not just
fail-safe.

-- 
Gaëtan Rivet
6WIND