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

[Elad Nachman <eladv6@gmail.com>]

1. Userspace will get an error
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.

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?
> >>
> >>
>
>