From: Elad Nachman <eladv6@gmail.com>
To: Ferruh Yigit <ferruh.yigit@intel.com>
Cc: Eric Christian <erclists@gmail.com>, dev <dev@dpdk.org>,
Igor Ryzhov <iryzhov@nfware.com>
Subject: Re: [dpdk-dev] [PATCH v2] kni: Fix request overwritten
Date: Mon, 4 Oct 2021 19:18:53 +0300 [thread overview]
Message-ID: <CACXF7qnqp=hdbvZSq5psbmcaTdYTPvXV0N7rqirvpEGPKBNpGg@mail.gmail.com> (raw)
In-Reply-To: <8525082f-eb28-92db-11d3-ef4d24144be4@intel.com>
On Mon, Oct 4, 2021 at 7:05 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> On 10/4/2021 3:58 PM, Elad Nachman wrote:
> > 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.
> >
>
> Not sure if it will reach to the end user. If user is calling "ifconfig
> <iface>
> down", it will just fail right, it won't recognize the error type.
>
> Unless this is common usage by the Linux network drivers, having this
> usage in
> KNI won't help much. I am for handling this in the kernel side if we can.
>
>
If user calls ifconfig <iface> down it will not happen. It requires some
multi-core race condition only Eric can recreate.
> >>
> >>> 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.
> >
>
> (sure you like short answers)
>
> Please help me to see why "interface down" is special. Isn't it point of
> your
> patch to wait the request execution in the userspace even it is an async
> request?
>
> And yet again, number of retry can be limited.
>
>
No, it is not. Please look again:
https://patches.dpdk.org/project/dpdk/patch/20210924105409.21711-1-eladv6@gmail.com/
>
> >
> >> 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.
>
>
next prev parent reply other threads:[~2021-10-04 16:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-24 10:54 Elad Nachman
2021-10-04 13:01 ` Ferruh Yigit
2021-10-04 13:09 ` Elad Nachman
2021-10-04 14:03 ` Ferruh Yigit
2021-10-04 14:25 ` Elad Nachman
2021-10-04 14:51 ` Ferruh Yigit
2021-10-04 14:58 ` Elad Nachman
2021-10-04 15:48 ` Ferruh Yigit
2021-10-04 16:18 ` Elad Nachman [this message]
2021-10-04 16:59 ` Eric Christian
2021-10-04 18:27 ` Elad Nachman
2021-10-08 20:23 ` Ferruh Yigit
2021-10-08 21:11 ` Ferruh Yigit
2021-10-04 14:14 ` Eric Christian
2021-10-04 14:56 ` Ferruh Yigit
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CACXF7qnqp=hdbvZSq5psbmcaTdYTPvXV0N7rqirvpEGPKBNpGg@mail.gmail.com' \
--to=eladv6@gmail.com \
--cc=dev@dpdk.org \
--cc=erclists@gmail.com \
--cc=ferruh.yigit@intel.com \
--cc=iryzhov@nfware.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).