Re: [dpdk-dev] [PATCH v2] kni: Fix request overwritten

[Elad Nachman <eladv6@gmail.com>]

בתאריך יום ב׳, 4 באוק׳ 2021, 17:51, מאת Ferruh Yigit ‏<
ferruh.yigit@intel.com>:

> On 10/4/2021 3:25 PM, Elad Nachman wrote:
>
> Can you please try to not top post, it will make impossible to follow this
> discussion later from the mail archives.
>
> > 1. Userspace will get an error
>
> So there is nothing special with returning '-EAGAIN', user will only
> observe an
> error.
> Wasn't initial intention to use '-EAGAIN' to try request again?
>
> To signal user-space to retry the operation.

>
> > 2. Waiting with rtnl locked causes a deadlock; waiting with rtnl unlocked
> > for interface down command causes a crash because of a race condition in
> > the device delete/unregister list in the kernel.
> >
>
> Why waiting with rthnl lock causes a deadlock? As said below we are already
> doing it, why it is different with retry logic?
>
> Because it can be interface down request.


> I agree to not wait with rtnl unlocked.
>
> > FYI,
> >
> > Elad.
> >
> > בתאריך יום ב׳, 4 באוק׳ 2021, 17:13, מאת Ferruh Yigit ‏<
> > ferruh.yigit@intel.com>:
> >
> >> On 10/4/2021 2:09 PM, Elad Nachman wrote:
> >>> Hi,
> >>>
> >>> EAGAIN is propogated back to the kernel and to the caller.
> >>>
> >>
> >> So will the user get an error, or it will be handled by the kernel and
> >> retried?
> >>
> >>> We cannot retry from the kni kernel module since we hold the rtnl lock.
> >>>
> >>
> >> Why not? We are already waiting until a command time out, like
> >> 'kni_net_open()'
> >> can retry if 'kni_net_process_request()' returns '-EAGAIN'. And we can
> >> limit the
> >> number of retry for safety.
> >>
> >>> FYI,
> >>>
> >>> Elad
> >>>
> >>> בתאריך יום ב׳, 4 באוק׳ 2021, 16:05, מאת Ferruh Yigit ‏<
> >>> ferruh.yigit@intel.com>:
> >>>
> >>>> On 9/24/2021 11:54 AM, Elad Nachman wrote:
> >>>>> Fix lack of multiple KNI requests handling support by introducing a
> >>>>> request in progress flag which will fail additional requests with
> >>>>> EAGAIN return code if the original request has not been processed
> >>>>> by user-space.
> >>>>>
> >>>>> Bugzilla ID: 809
> >>>>
> >>>> Hi Eric,
> >>>>
> >>>> Can you please test this patch, if it solves the issue you reported?
> >>>>
> >>>>>
> >>>>> Signed-off-by: Elad Nachman <eladv6@gmail.com>
> >>>>> ---
> >>>>>  kernel/linux/kni/kni_net.c | 9 +++++++++
> >>>>>  lib/kni/rte_kni.c          | 2 ++
> >>>>>  lib/kni/rte_kni_common.h   | 1 +
> >>>>>  3 files changed, 12 insertions(+)
> >>>>>
> >>>>
> >>>> <...>
> >>>>
> >>>>> @@ -123,7 +124,15 @@ kni_net_process_request(struct net_device *dev,
> >>>> struct rte_kni_request *req)
> >>>>>
> >>>>>       mutex_lock(&kni->sync_lock);
> >>>>>
> >>>>> +     /* Check that existing request has been processed: */
> >>>>> +     cur_req = (struct rte_kni_request *)kni->sync_kva;
> >>>>> +     if (cur_req->req_in_progress) {
> >>>>> +             ret = -EAGAIN;
> >>>>
> >>>> Overall logic in the KNI looks good to me, this helps to serialize the
> >>>> requests
> >>>> even for async ones.
> >>>>
> >>>> But can you please clarify how it behaves in the kernel side with
> >> '-EAGAIN'
> >>>> return type? Will linux call the ndo again, or will it just fail.
> >>>>
> >>>> If it just fails should we handle the re-try on '-EAGAIN' within the
> kni
> >>>> module?
> >>>>
> >>>>
> >>
> >>
>
> Elad.