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 07:45:44 +0200 Message-ID: <20151013054543.GB2242@nanopsycho.orion> References: <1444672467-20621-1-git-send-email-jiri@resnulli.us> <1444672986-20709-1-git-send-email-jiri@resnulli.us> <561C8B39.20604@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Scott Feldman , Netdev , "David S. Miller" , Ido Schimmel , Elad Raz , Florian Fainelli , Guenter Roeck , Vivien Didelot , "andrew@lunn.ch" , David Laight , "stephen@networkplumber.org" To: John Fastabend Return-path: Received: from mail-wi0-f174.google.com ([209.85.212.174]:36917 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbbJMFpq (ORCPT ); Tue, 13 Oct 2015 01:45:46 -0400 Received: by wijq8 with SMTP id q8so13914175wij.0 for ; Mon, 12 Oct 2015 22:45:45 -0700 (PDT) Content-Disposition: inline In-Reply-To: <561C8B39.20604@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: Tue, Oct 13, 2015 at 06:40:25AM CEST, john.fastabend@gmail.com wrote: >On 15-10-12 07:52 PM, Scott Feldman 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. >> >>> 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. >> > >Also an additional race between setting rtnl_locked and the if stmt >and then grabbing the lock. There seems to be a something of pattern >around this where other subsystems use a rtnl_trylock and if it fails >do a restart/re-queue operation to retry. Looks like how you handle >it in the team driver at least. No, this is for different case. This is for case someone calls switchdev_flush_defererd holding the rtnl_lock. > >>> + err = switchdev_port_attr_set_now(asw->dev, &asw->attr); >>> if (err && err != -EOPNOTSUPP) >>> netdev_err(asw->dev, "failed (err=%d) to set attribute (id=%d)\n", >>> err, asw->attr.id); >>> - rtnl_unlock(); >>> + if (!rtnl_locked) >>> + rtnl_unlock(); >>> >>> dev_put(asw->dev); >>> kfree(work); >>> @@ -211,7 +257,7 @@ static int switchdev_port_attr_set_defer(struct net_device *dev, >>> asw->dev = dev; >>> memcpy(&asw->attr, attr, sizeof(asw->attr)); >>> >>> - schedule_work(&asw->work); >>> + queue_work(switchdev_wq, &asw->work); >>> >>> return 0; >>> } >