From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Pirko Subject: Re: [patch net-next v4 2/7] switchdev: allow caller to explicitly request attr_set as deferred Date: Tue, 13 Oct 2015 09:30:20 +0200 Message-ID: <20151013073020.GF2242@nanopsycho.orion> References: <1444672467-20621-1-git-send-email-jiri@resnulli.us> <1444672986-20709-1-git-send-email-jiri@resnulli.us> <20151013054414.GA2242@nanopsycho.orion> <561C9EC2.7030907@gmail.com> <20151013062112.GD2242@nanopsycho.orion> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: John Fastabend , Netdev , "David S. Miller" , Ido Schimmel , Elad Raz , Florian Fainelli , Guenter Roeck , Vivien Didelot , "andrew@lunn.ch" , David Laight , "stephen@networkplumber.org" To: Scott Feldman Return-path: Received: from mail-wi0-f175.google.com ([209.85.212.175]:34896 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbbJMHaY (ORCPT ); Tue, 13 Oct 2015 03:30:24 -0400 Received: by wicge5 with SMTP id ge5so177698761wic.0 for ; Tue, 13 Oct 2015 00:30:23 -0700 (PDT) Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Tue, Oct 13, 2015 at 08:53:45AM CEST, sfeldma@gmail.com wrote: >On Mon, Oct 12, 2015 at 11:21 PM, Jiri Pirko wrote: >> Tue, Oct 13, 2015 at 08:03:46AM CEST, john.fastabend@gmail.com wrote: >>>On 15-10-12 10:44 PM, Jiri Pirko wrote: >>>> Tue, Oct 13, 2015 at 04:52:42AM CEST, sfeldma@gmail.com wrote: >>>>> On Mon, Oct 12, 2015 at 11:03 AM, Jiri Pirko wrote: >>>>>> From: Jiri Pirko >>>>>> >>>>>> Caller should know if he can call attr_set directly (when holding RTNL) >>>>>> or if he has to defer the att_set processing for later. >>>>>> >>>>>> This also allows drivers to sleep inside attr_set and report operation >>>>>> status back to switchdev core. Switchdev core then warns if status is >>>>>> not ok, instead of silent errors happening in drivers. >>>>>> >>>>>> Signed-off-by: Jiri Pirko >>>>>> --- >>>>>> include/net/switchdev.h | 1 + >>>>>> net/bridge/br_stp.c | 3 +- >>>>>> net/switchdev/switchdev.c | 107 ++++++++++++++++++++++++---------------------- >>>>>> 3 files changed, 59 insertions(+), 52 deletions(-) >>>>>> >>>>>> diff --git a/include/net/switchdev.h b/include/net/switchdev.h >>>>>> index d2879f2..6b109e4 100644 >>>>>> --- a/include/net/switchdev.h >>>>>> +++ b/include/net/switchdev.h >>>>>> @@ -17,6 +17,7 @@ >>>>>> >>>>>> #define SWITCHDEV_F_NO_RECURSE BIT(0) >>>>>> #define SWITCHDEV_F_SKIP_EOPNOTSUPP BIT(1) >>>>>> +#define SWITCHDEV_F_DEFER BIT(2) >>>>>> >>>>>> struct switchdev_trans_item { >>>>>> struct list_head list; >>>>>> diff --git a/net/bridge/br_stp.c b/net/bridge/br_stp.c >>>>>> index db6d243de..80c34d7 100644 >>>>>> --- a/net/bridge/br_stp.c >>>>>> +++ b/net/bridge/br_stp.c >>>>>> @@ -41,13 +41,14 @@ void br_set_state(struct net_bridge_port *p, unsigned int state) >>>>>> { >>>>>> struct switchdev_attr attr = { >>>>>> .id = SWITCHDEV_ATTR_ID_PORT_STP_STATE, >>>>>> + .flags = SWITCHDEV_F_DEFER, >>>>>> .u.stp_state = state, >>>>>> }; >>>>>> int err; >>>>>> >>>>>> p->state = state; >>>>>> err = switchdev_port_attr_set(p->dev, &attr); >>>>>> - if (err && err != -EOPNOTSUPP) >>>>>> + if (err) >>>>> >>>>> This looks like a problem as now all other non-switchdev ports will >>>>> get an WARN in the log when STP state changes. We should only WARN if >>>>> there was an err and the err is not -EOPNOTSUPP. >>>> >>>> If SWITCHDEV_F_DEFER flag is set, there's only 0 of -ENOMEM. >>>> >>>> >>>>> >>>>>> br_warn(p->br, "error setting offload STP state on port %u(%s)\n", >>>>>> (unsigned int) p->port_no, p->dev->name); >>>>>> } >>>>> >>>>> >>>>> >>>>>> struct switchdev_attr_set_work { >>>>>> struct work_struct work; >>>>>> struct net_device *dev; >>>>>> @@ -183,14 +226,17 @@ static void switchdev_port_attr_set_work(struct work_struct *work) >>>>>> { >>>>>> struct switchdev_attr_set_work *asw = >>>>>> container_of(work, struct switchdev_attr_set_work, work); >>>>>> + bool rtnl_locked = rtnl_is_locked(); >>>>>> int err; >>>>>> >>>>>> - rtnl_lock(); >>>>>> - err = switchdev_port_attr_set(asw->dev, &asw->attr); >>>>>> + if (!rtnl_locked) >>>>>> + rtnl_lock(); >>>>> >>>>> I'm not following this change. If someone else has rtnl_lock, we'll >>>>> not wait to grab it here ourselves, and proceed as if we have the >>>>> lock. But what if that someone else releases the lock in the middle >>>>> of us doing switchdev_port_attr_set_now? Seems we want to >>>>> unconditionally wait and grab the lock. We need to block anything >>>>>from moving while we do the attr set. >>>> >>>> Why would someone we call (driver) return the lock? In that case, he is >>>> buggy and should be fixed. >>>> >>>> This hunk only ensures we have rtnl_lock. If not, we take it here. We do >>>> not take it unconditionally because we may already have it, for example >>>> if caller of switchdev_flush_deferred holds rtnl_lock. >>>> >>> >>>This is where you lost me. How do you know another core doesn't happen >>>to have the lock when you hit this code path? Maybe someone is running >>>an ethtool command on another core or something. >> >> You are right. The same problem exists currently in switchdev_port_attr_set. > >You are right as in you'll change this back to unconditional grabbing >of rtnl_lock? I don't follow how this problem currently exists as >current code does an unconditional grab of rtnl_lock. cpu1 cpu2 rtnl_lock() switchdev_port_attr_set !rtnl_is_locked() == false switchdev_trans_init rtnl_unlock() __switchdev_port_attr_set now __switchdev_port_attr_set is called without rtnl_lock. Would make sense to introduce rtnl_is_locked_by_me() or something.