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Miller" , Andrew Lunn , Vivien Didelot , Florian Fainelli , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bridge@lists.linux-foundation.org, Roopa Prabhu , Jiri Pirko , Claudiu Manoil , Alexandre Belloni , UNGLinuxDriver@microchip.com, Vadym Kochan , Taras Chornyi , Grygorii Strashko , Ioana Ciornei , Ivan Vecera , linux-omap@vger.kernel.org Subject: Re: [PATCH v3 net-next 00/11] Cleanup in brport flags switchdev offload for DSA Message-ID: <20210210125923.GA296172@shredder.lan> References: <20210210104549.ga3lgjafn5x3htwj@skbuf> <20210210110125.rw6fvjtsqmmuglcg@skbuf> <90b255e6-efd2-b234-7bfc-4285331e56b1@nvidia.com> <20210210120106.g7blqje3wq4j5l6j@skbuf> <20210210122105.GA294287@shredder.lan> <20210210122936.rpvdh7ksjfh2ee6b@skbuf> <20210210123823.GA294900@shredder.lan> <20210210125501.f6lbfv5y5zj4qrmi@skbuf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210210125501.f6lbfv5y5zj4qrmi@skbuf> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 10, 2021 at 02:55:01PM +0200, Vladimir Oltean wrote: > On Wed, Feb 10, 2021 at 02:38:23PM +0200, Ido Schimmel wrote: > > On Wed, Feb 10, 2021 at 02:29:36PM +0200, Vladimir Oltean wrote: > > > On Wed, Feb 10, 2021 at 02:21:05PM +0200, Ido Schimmel wrote: > > > > On Wed, Feb 10, 2021 at 02:01:06PM +0200, Vladimir Oltean wrote: > > > > > 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 > > > > > > > > Can you please point to the bug? I'm not following > > > > > > For example, mlxsw eventually calls mlxsw_sp_fid_flood_set from the > > > SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS handling data path, and this > > > function allocates memory with GFP_KERNEL. > > > > > > Another example is prestera which eventually calls prestera_fw_send_req > > > which takes a mutex_lock. > > > > > > Yet another example are mv88e6xxx and b53 which use MDIO and SPI > > > from their .port_egress_floods implementation, buses which have > > > might_sleep() in them. > > > > Right, but see the code: > > > > ``` > > attr.id = SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS; > > attr.flags = SWITCHDEV_F_DEFER; > > attr.u.brport_flags = flags; > > > > err = switchdev_port_attr_set(p->dev, &attr); > > ``` > > > > And check how SWITCHDEV_F_DEFER is used. > > > > We can squash SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS and > > SWITCHDEV_ATTR_ID_PORT_PRE_BRIDGE_FLAGS into one blocking notification > > by reducing the scope of the bridge lock like Nik suggested. Currently > > it's just blindly taken around br_setport(). > > Okay, so the deferred attr_set propagates just a possible ENOMEM from > the deferred work enqueue, not the actual failure if that occurred. > > I can leave alone the piece that sends two notifications for now, but I > would still need to deliver the full struct switchdev_brport_flags with > both the flags and the mask to both the PRE_BRIDGE_FLAGS and the > BRIDGE_FLAGS, because I need to deliver an extack from the sja1105 driver > that BR_FLOOD should always have the same value as BR_MCAST_FLOOD. OK