From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C874C433EF for ; Wed, 18 May 2022 13:08:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237468AbiERNIl (ORCPT ); Wed, 18 May 2022 09:08:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237418AbiERNIk (ORCPT ); Wed, 18 May 2022 09:08:40 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C5588179C36 for ; Wed, 18 May 2022 06:08:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652879317; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wEVU18jGfqPcmg2q4iHtheDOMAbASwTYENcJwOv1TWc=; b=Sk0ApSouRO4FUI2imf3bDGbi2tq1XloAR6XDtl9Gt6vuz8NvWp9b8Hd0vqsT6sHpX7+vZb zT60+eIBLMBcEUS8jCcgK8ZslZ+oXne2XYujNYkh46XGIXSCV7OApwq3waRceslCYZgqvU xsV7E7I1VVhOKgUC5xWO4i2acbyuR2c= Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-528-zCnmabxiOn2uM3qDFS_vAA-1; Wed, 18 May 2022 09:08:35 -0400 X-MC-Unique: zCnmabxiOn2uM3qDFS_vAA-1 Received: by mail-qk1-f199.google.com with SMTP id bl27-20020a05620a1a9b00b0069994eeb30cso1495371qkb.11 for ; Wed, 18 May 2022 06:08:35 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=wEVU18jGfqPcmg2q4iHtheDOMAbASwTYENcJwOv1TWc=; b=H1Qa954UuqSsub2xSBqfffAUNrHHhjoaq4UWWPz3DxKIc34gLBY2am8wO8g/bqs4Qg O5I8mbUCZC3FxkeQDIA+sqe7lB1JbXp0bzaeHhx1qeIPIVZaQjb/dZuI069dIhZN71pz S6zXzT0nMiGlHnxagzJGnmc1i3wfsX6V2dnRU2PuXjZSmUrphVjXpR71gQfG6W2ThY+b 7+bYB+n2kPAHszr+/CFPmqLDesu7KQJ3Msq8kNu6T6S3yR36pW7GcpeR7LcU1QofqL3C JnqIzmAphW1TISEJZ5RRXBaVZx6XCJ0WqG06bvggi/V9u0rVvFwxaaDlKwyIEcF4Ol7Z gimg== X-Gm-Message-State: AOAM531vuuVnCvAFA91HrOUxjWdhQo6xC9u822+48GMKWDwR+vYbWZmG zkI0X6nyJz7sks7mkibfs5I7z8J5CKY8j1Eq97ms0fp6qE497aDOMDCeLa+DKwv+su4wDtrAW4i 2p6qv9YVwIgI5OC4qXEVbhoJ1TdsBntYScU7nIQ== X-Received: by 2002:a05:6214:c29:b0:45a:fedd:7315 with SMTP id a9-20020a0562140c2900b0045afedd7315mr24139576qvd.59.1652879314835; Wed, 18 May 2022 06:08:34 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwTj9VLJa4E8oodXN1Ll3A3AwZmkLpQENC3BMYxCu0fDFABePD1WxXu6gjHoJfmlEpF13d6AdaQMKuUrBi/PVk= X-Received: by 2002:a05:6214:c29:b0:45a:fedd:7315 with SMTP id a9-20020a0562140c2900b0045afedd7315mr24139548qvd.59.1652879314558; Wed, 18 May 2022 06:08:34 -0700 (PDT) MIME-Version: 1.0 References: <20220512143314.235604-1-miquel.raynal@bootlin.com> <20220512143314.235604-10-miquel.raynal@bootlin.com> <20220517153045.73fda4ee@xps-13> <20220518121200.2f08a6b1@xps-13> <20220518143702.48cb9c66@xps-13> In-Reply-To: <20220518143702.48cb9c66@xps-13> From: Alexander Aring Date: Wed, 18 May 2022 09:08:23 -0400 Message-ID: Subject: Re: [PATCH wpan-next v2 09/11] net: mac802154: Introduce a synchronous API for MLME commands To: Miquel Raynal Cc: Alexander Aring , Stefan Schmidt , linux-wpan - ML , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Network Development , David Girault , Romuald Despres , Frederic Blain , Nicolas Schodet , Thomas Petazzoni Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-wpan@vger.kernel.org Hi, On Wed, May 18, 2022 at 8:37 AM Miquel Raynal wrote: > > > alex.aring@gmail.com wrote on Wed, 18 May 2022 08:05:46 -0400: > > > Hi, > > > > On Wed, May 18, 2022 at 6:12 AM Miquel Raynal wrote: > > > > > > > > > aahringo@redhat.com wrote on Tue, 17 May 2022 21:14:03 -0400: > > > > > > > Hi, > > > > > > > > On Tue, May 17, 2022 at 9:30 AM Miquel Raynal wrote: > > > > > > > > > > > > > > > aahringo@redhat.com wrote on Sun, 15 May 2022 19:03:53 -0400: > > > > > > > > > > > Hi, > > > > > > > > > > > > On Sun, May 15, 2022 at 6:28 PM Alexander Aring wrote: > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > On Thu, May 12, 2022 at 10:34 AM Miquel Raynal > > > > > > > wrote: > > > > > > > > > > > > > > > > This is the slow path, we need to wait for each command to be processed > > > > > > > > before continuing so let's introduce an helper which does the > > > > > > > > transmission and blocks until it gets notified of its asynchronous > > > > > > > > completion. This helper is going to be used when introducing scan > > > > > > > > support. > > > > > > > > > > > > > > > > Signed-off-by: Miquel Raynal > > > > > > > > --- > > > > > > > > net/mac802154/ieee802154_i.h | 1 + > > > > > > > > net/mac802154/tx.c | 25 +++++++++++++++++++++++++ > > > > > > > > 2 files changed, 26 insertions(+) > > > > > > > > > > > > > > > > diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h > > > > > > > > index a057827fc48a..f8b374810a11 100644 > > > > > > > > --- a/net/mac802154/ieee802154_i.h > > > > > > > > +++ b/net/mac802154/ieee802154_i.h > > > > > > > > @@ -125,6 +125,7 @@ extern struct ieee802154_mlme_ops mac802154_mlme_wpan; > > > > > > > > void ieee802154_rx(struct ieee802154_local *local, struct sk_buff *skb); > > > > > > > > void ieee802154_xmit_sync_worker(struct work_struct *work); > > > > > > > > int ieee802154_sync_and_hold_queue(struct ieee802154_local *local); > > > > > > > > +int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *skb); > > > > > > > > netdev_tx_t > > > > > > > > ieee802154_monitor_start_xmit(struct sk_buff *skb, struct net_device *dev); > > > > > > > > netdev_tx_t > > > > > > > > diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c > > > > > > > > index 38f74b8b6740..ec8d872143ee 100644 > > > > > > > > --- a/net/mac802154/tx.c > > > > > > > > +++ b/net/mac802154/tx.c > > > > > > > > @@ -128,6 +128,31 @@ int ieee802154_sync_and_hold_queue(struct ieee802154_local *local) > > > > > > > > return ieee802154_sync_queue(local); > > > > > > > > } > > > > > > > > > > > > > > > > +int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *skb) > > > > > > > > +{ > > > > > > > > + int ret; > > > > > > > > + > > > > > > > > + /* Avoid possible calls to ->ndo_stop() when we asynchronously perform > > > > > > > > + * MLME transmissions. > > > > > > > > + */ > > > > > > > > + rtnl_lock(); > > > > > > > > > > > > > > I think we should make an ASSERT_RTNL() here, the lock needs to be > > > > > > > earlier than that over the whole MLME op. MLME can trigger more than > > > > > > > > > > > > not over the whole MLME_op, that's terrible to hold the rtnl lock so > > > > > > long... so I think this is fine that some netdev call will interfere > > > > > > with this transmission. > > > > > > So forget about the ASSERT_RTNL() here, it's fine (I hope). > > > > > > > > > > > > > one message, the whole sync_hold/release queue should be earlier than > > > > > > > that... in my opinion is it not right to allow other messages so far > > > > > > > an MLME op is going on? I am not sure what the standard says to this, > > > > > > > but I think it should be stopped the whole time? All those sequence > > > > > > > > > > > > Whereas the stop of the netdev queue makes sense for the whole mlme-op > > > > > > (in my opinion). > > > > > > > > > > I might still implement an MLME pre/post helper and do the queue > > > > > hold/release calls there, while only taking the rtnl from the _tx. > > > > > > > > > > And I might create an mlme_tx_one() which does the pre/post calls as > > > > > well. > > > > > > > > > > Would something like this fit? > > > > > > > > I think so, I've heard for some transceiver types a scan operation can > > > > take hours... but I guess whoever triggers that scan in such an > > > > environment knows that it has some "side-effects"... > > > > > > Yeah, a scan requires the data queue to be stopped and all incoming > > > packets to be dropped (others than beacons, ofc), so users must be > > > aware of this limitation. > > > > I think there is a real problem about how the user can synchronize the > > start of a scan and be sure that at this point everything was > > transmitted, we might need to real "flush" the queue. Your naming > > "flush" is also wrong, It will flush the framebuffer(s) of the > > transceivers but not the netdev queue... and we probably should flush > > the netdev queue before starting mlme-op... this is something to add > > in the mlme_op_pre() function. > > Is it even possible? This requires waiting for the netdev queue to be > empty before stopping it, but if users constantly flood the transceiver > with data packets this might "never" happen. > Nothing is impossible, just maybe nobody thought about that. Sure putting more into the queue should be forbidden but what's inside should be "flushed". Currently we make a hard cut, there is no way that the user knows what's sent or not BUT that is the case for xmit_do() anyway, it's not reliable... people need to have the right upper layer protocol. However I think we could run into problems if we especially have features like waiting for the socket error queue to know if e.g. an ack was received or not. > And event thought we might accept this situation, I don't know how to > check the emptiness of the netif queue. Any inputs? Don't think about it, I see a practical issue here which I keep in my mind. - Alex