From: Vladimir Oltean <olteanv@gmail.com>
To: Nikolay Aleksandrov <nikolay@nvidia.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Andrew Lunn <andrew@lunn.ch>,
Vivien Didelot <vivien.didelot@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bridge@lists.linux-foundation.org,
Roopa Prabhu <roopa@nvidia.com>, Jiri Pirko <jiri@resnulli.us>,
Ido Schimmel <idosch@idosch.org>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
UNGLinuxDriver@microchip.com, Vadym Kochan <vkochan@marvell.com>,
Taras Chornyi <tchornyi@marvell.com>,
Grygorii Strashko <grygorii.strashko@ti.com>,
Ioana Ciornei <ioana.ciornei@nxp.com>,
Ivan Vecera <ivecera@redhat.com>,
linux-omap@vger.kernel.org
Subject: Re: [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA
Date: Wed, 10 Feb 2021 14:01:06 +0200 [thread overview]
Message-ID: <20210210120106.g7blqje3wq4j5l6j@skbuf> (raw)
In-Reply-To: <90b255e6-efd2-b234-7bfc-4285331e56b1@nvidia.com>
On Wed, Feb 10, 2021 at 01:05:57PM +0200, Nikolay Aleksandrov wrote:
> On 10/02/2021 13:01, Vladimir Oltean wrote:
> > On Wed, Feb 10, 2021 at 12:52:33PM +0200, Nikolay Aleksandrov wrote:
> >> On 10/02/2021 12:45, Vladimir Oltean wrote:
> >>> Hi Nikolay,
> >>>
> >>> On Wed, Feb 10, 2021 at 12:31:43PM +0200, Nikolay Aleksandrov wrote:
> >>>> Hi Vladimir,
> >>>> Let's take a step back for a moment and discuss the bridge unlock/lock sequences
> >>>> that come with this set. I'd really like to avoid those as they're a recipe
> >>>> for future problems. The only good way to achieve that currently is to keep
> >>>> the PRE_FLAGS call and do that in unsleepable context but move the FLAGS call
> >>>> after the flags have been changed (if they have changed obviously). That would
> >>>> make the code read much easier since we'll have all our lock/unlock sequences
> >>>> in the same code blocks and won't play games to get sleepable context.
> >>>> Please let's think and work in that direction, rather than having:
> >>>> + spin_lock_bh(&p->br->lock);
> >>>> + if (err) {
> >>>> + netdev_err(p->dev, "%s\n", extack._msg);
> >>>> + return err;
> >>>> }
> >>>> +
> >>>>
> >>>> which immediately looks like a bug even though after some code checking we can
> >>>> verify it's ok. WDYT?
> >>>>
> >>>> I plan to get rid of most of the br->lock since it's been abused for a very long
> >>>> time because it's essentially STP lock, but people have started using it for other
> >>>> things and I plan to fix that when I get more time.
> >>>
> >>> This won't make the sysfs codepath any nicer, will it?
> >>>
> >>
> >> Currently we'll have to live with a hack that checks if the flags have changed. I agree
> >> it won't be pretty, but we won't have to unlock and lock again in the middle of the
> >> called function and we'll have all our locking in the same place, easier to verify and
> >> later easier to remove. Once I get rid of most of the br->lock usage we can revisit
> >> the drop of PRE_FLAGS if it's a problem. The alternative is to change the flags, then
> >> send the switchdev notification outside of the lock and revert the flags if it doesn't
> >> go through which doesn't sound much better.
> >> I'm open to any other suggestions, but definitely would like to avoid playing locking games.
> >> Even if it means casing out flag setting from all other store_ functions for sysfs.
> >
> > By casing out flag settings you mean something like this?
> >
> >
> > #define BRPORT_ATTR(_name, _mode, _show, _store) \
> > const struct brport_attribute brport_attr_##_name = { \
> > .attr = {.name = __stringify(_name), \
> > .mode = _mode }, \
> > .show = _show, \
> > .store_unlocked = _store, \
> > };
> >
> > #define BRPORT_ATTR_FLAG(_name, _mask) \
> > static ssize_t show_##_name(struct net_bridge_port *p, char *buf) \
> > { \
> > return sprintf(buf, "%d\n", !!(p->flags & _mask)); \
> > } \
> > static int store_##_name(struct net_bridge_port *p, unsigned long v) \
> > { \
> > return store_flag(p, v, _mask); \
> > } \
> > static BRPORT_ATTR(_name, 0644, \
> > show_##_name, store_##_name)
> >
> > static ssize_t brport_store(struct kobject *kobj,
> > struct attribute *attr,
> > const char *buf, size_t count)
> > {
> > ...
> >
> > } else if (brport_attr->store_unlocked) {
> > val = simple_strtoul(buf, &endp, 0);
> > if (endp == buf)
> > goto out_unlock;
> > ret = brport_attr->store_unlocked(p, val);
> > }
> >
>
> Yes, this can work but will need a bit more changes because of br_port_flags_change().
> Then the netlink side can be modeled in a similar way.
What I just don't understand is how others can get away with doing
sleepable work in atomic context but I can't make the notifier blocking
by dropping a spinlock which isn't needed there, because it looks ugly :D
next prev parent reply other threads:[~2021-02-10 12:04 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 9:14 [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA Vladimir Oltean
2021-02-10 9:14 ` [PATCH v3 net-next 01/11] net: switchdev: propagate extack to port attributes Vladimir Oltean
2021-02-11 4:12 ` Florian Fainelli
2021-02-10 9:14 ` [PATCH v3 net-next 02/11] net: bridge: offload all port flags at once in br_setport Vladimir Oltean
2021-02-10 9:14 ` [PATCH v3 net-next 03/11] net: bridge: don't print in br_switchdev_set_port_flag Vladimir Oltean
2021-02-10 9:14 ` [PATCH v3 net-next 04/11] net: dsa: configure proper brport flags when ports leave the bridge Vladimir Oltean
2021-02-11 4:16 ` Florian Fainelli
2021-02-10 9:14 ` [PATCH v3 net-next 05/11] net: squash switchdev attributes PRE_BRIDGE_FLAGS and BRIDGE_FLAGS Vladimir Oltean
2021-02-10 9:14 ` [PATCH v3 net-next 06/11] net: dsa: kill .port_egress_floods overengineering Vladimir Oltean
2021-02-11 4:18 ` Florian Fainelli
2021-02-10 9:14 ` [PATCH v3 net-next 07/11] net: prep switchdev drivers for concurrent SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS Vladimir Oltean
2021-02-10 10:12 ` Ido Schimmel
2021-02-10 10:23 ` Vladimir Oltean
2021-02-10 23:34 ` David Miller
2021-02-10 9:14 ` [PATCH v3 net-next 08/11] net: bridge: put SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS on the blocking call chain Vladimir Oltean
2021-02-10 10:14 ` Nikolay Aleksandrov
2021-02-10 9:14 ` [PATCH v3 net-next 09/11] net: mscc: ocelot: use separate flooding PGID for broadcast Vladimir Oltean
2021-02-11 4:19 ` Florian Fainelli
2021-02-10 9:14 ` [PATCH v3 net-next 10/11] net: mscc: ocelot: offload bridge port flags to device Vladimir Oltean
2021-02-11 4:20 ` Florian Fainelli
2021-02-10 9:14 ` [PATCH v3 net-next 11/11] net: dsa: sja1105: " Vladimir Oltean
2021-02-10 10:31 ` [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA Nikolay Aleksandrov
2021-02-10 10:45 ` Vladimir Oltean
2021-02-10 10:52 ` Nikolay Aleksandrov
2021-02-10 11:01 ` Vladimir Oltean
2021-02-10 11:05 ` Nikolay Aleksandrov
2021-02-10 12:01 ` Vladimir Oltean [this message]
2021-02-10 12:10 ` Nikolay Aleksandrov
2021-02-10 12:21 ` Ido Schimmel
2021-02-10 12:29 ` Vladimir Oltean
2021-02-10 12:38 ` Ido Schimmel
2021-02-10 12:55 ` Vladimir Oltean
2021-02-10 12:59 ` Ido Schimmel
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