From: Nikolay Aleksandrov <nikolay@nvidia.com>
To: Vladimir Oltean <olteanv@gmail.com>,
Jakub Kicinski <kuba@kernel.org>,
"David S. Miller" <davem@davemloft.net>
Cc: 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 08/11] net: bridge: put SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS on the blocking call chain
Date: Wed, 10 Feb 2021 12:14:06 +0200 [thread overview]
Message-ID: <0208ba7c-601b-de5c-1922-c6d1911501a1@nvidia.com> (raw)
In-Reply-To: <20210210091445.741269-9-olteanv@gmail.com>
On 10/02/2021 11:14, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>
> Since we would like br_switchdev_set_port_flag to not use an atomic
> notifier, it should be called from outside spinlock context.
>
> We can temporarily drop br->lock, but that creates some concurrency
> complications (example below is given for sysfs):
> - There might be an "echo 1 > multicast_flood" simultaneous with an
> "echo 0 > multicast_flood". The result of this is nondeterministic
> either way, so I'm not too concerned as long as the result is
> consistent (no other flags have changed).
> - There might be an "echo 1 > multicast_flood" simultaneous with an
> "echo 0 > learning". My expectation is that none of the two writes are
> "eaten", and the final flags contain BR_MCAST_FLOOD=1 and BR_LEARNING=0
> regardless of the order of execution. That is actually possible if, on
> the commit path, we don't do a trivial "p->flags = flags" which might
> overwrite bits outside of our mask, but instead we just change the
> flags corresponding to our mask.
>
Not sure I follow here, how do we get any concurrency issues with sysfs or netlink
when both take rtnl before doing any changes ?
> Now that br_switchdev_set_port_flag is never called from under br->lock,
> it runs in sleepable context.
>
> All switchdev drivers handle SWITCHDEV_PORT_ATTR_SET as both blocking
> and atomic, so no changes are needed on that front.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> Changes in v3:
> - Drop the br->lock around br_switchdev_set_port_flag in this patch, for
> both sysfs and netlink.
> - Only set/restore the masked bits in p->flags to avoid concurrency
> issues.
>
> Changes in v2:
> Patch is new.
>
> net/bridge/br_netlink.c | 10 +++++++---
> net/bridge/br_switchdev.c | 5 ++---
> net/bridge/br_sysfs_if.c | 22 ++++++++++++++--------
> 3 files changed, 23 insertions(+), 14 deletions(-)
>
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index b7731614c036..8f09106966c4 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -869,7 +869,7 @@ static void br_set_port_flag(struct net_bridge_port *p, struct nlattr *tb[],
> static int br_setport(struct net_bridge_port *p, struct nlattr *tb[],
> struct netlink_ext_ack *extack)
> {
> - unsigned long old_flags, changed_mask;
> + unsigned long flags, old_flags, changed_mask;
> bool br_vlan_tunnel_old;
> int err;
>
> @@ -896,10 +896,14 @@ static int br_setport(struct net_bridge_port *p, struct nlattr *tb[],
> br_set_port_flag(p, tb, IFLA_BRPORT_ISOLATED, BR_ISOLATED);
>
> changed_mask = old_flags ^ p->flags;
> + flags = p->flags;
>
> - err = br_switchdev_set_port_flag(p, p->flags, changed_mask, extack);
> + spin_unlock_bh(&p->br->lock);
> + err = br_switchdev_set_port_flag(p, flags, changed_mask, extack);
> + spin_lock_bh(&p->br->lock);
> if (err) {
> - p->flags = old_flags;
> + p->flags &= ~changed_mask;
> + p->flags |= (old_flags & changed_mask);
> goto out;
> }
>
> diff --git a/net/bridge/br_switchdev.c b/net/bridge/br_switchdev.c
> index dbd94156960f..a79164ee65b9 100644
> --- a/net/bridge/br_switchdev.c
> +++ b/net/bridge/br_switchdev.c
> @@ -79,9 +79,8 @@ int br_switchdev_set_port_flag(struct net_bridge_port *p,
> attr.u.brport_flags.val = flags & mask;
> attr.u.brport_flags.mask = mask;
>
> - /* We run from atomic context here */
> - err = call_switchdev_notifiers(SWITCHDEV_PORT_ATTR_SET, p->dev,
> - &info.info, extack);
> + err = call_switchdev_blocking_notifiers(SWITCHDEV_PORT_ATTR_SET, p->dev,
> + &info.info, extack);
> err = notifier_to_errno(err);
> if (err == -EOPNOTSUPP)
> return 0;
> diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c
> index 72e92376eef1..3f21fdd1cdaa 100644
> --- a/net/bridge/br_sysfs_if.c
> +++ b/net/bridge/br_sysfs_if.c
> @@ -68,16 +68,22 @@ static int store_flag(struct net_bridge_port *p, unsigned long v,
> else
> flags &= ~mask;
>
> - if (flags != p->flags) {
> - err = br_switchdev_set_port_flag(p, flags, mask, &extack);
> - if (err) {
> - netdev_err(p->dev, "%s\n", extack._msg);
> - return err;
> - }
> + if (flags == p->flags)
> + return 0;
>
> - p->flags = flags;
> - br_port_flags_change(p, mask);
> + spin_unlock_bh(&p->br->lock);
> + err = br_switchdev_set_port_flag(p, flags, mask, &extack);
> + spin_lock_bh(&p->br->lock);
> + if (err) {
> + netdev_err(p->dev, "%s\n", extack._msg);
> + return err;
> }
> +
> + p->flags &= ~mask;
> + p->flags |= (flags & mask);
> +
> + br_port_flags_change(p, mask);
> +
> return 0;
> }
>
>
next prev parent reply other threads:[~2021-02-10 10:17 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 [this message]
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
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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