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Message-ID: <CAJpXRYReCbrh0z3fmgKqycJHZ+Z8=+KnK+YpOrhD1UsmgfiSxg@mail.gmail.com>
Date: Mon, 2 Sep 2024 09:34:48 +0200
From: Jonas Gorski <jonas.gorski@...dn.de>
To: Nikolay Aleksandrov <razor@...ckwall.org>
Cc: Ido Schimmel <idosch@...dia.com>, Roopa Prabhu <roopa@...dia.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Petr Machata <petrm@...lanox.com>,
Ido Schimmel <idosch@...lanox.com>, bridge@...ts.linux.dev, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: bridge: allow users setting EXT_LEARN for user
FDB entries
Am So., 1. Sept. 2024 um 14:25 Uhr schrieb Nikolay Aleksandrov
<razor@...ckwall.org>:
>
> On 01/09/2024 14:54, Ido Schimmel wrote:
> > On Sat, Aug 31, 2024 at 11:31:50AM +0300, Nikolay Aleksandrov wrote:
> >> On 30/08/2024 17:53, Jonas Gorski wrote:
> >>> When userspace wants to take over a fdb entry by setting it as
> >>> EXTERN_LEARNED, we set both flags BR_FDB_ADDED_BY_EXT_LEARN and
> >>> BR_FDB_ADDED_BY_USER in br_fdb_external_learn_add().
> >>>
> >>> If the bridge updates the entry later because its port changed, we clear
> >>> the BR_FDB_ADDED_BY_EXT_LEARN flag, but leave the BR_FDB_ADDED_BY_USER
> >>> flag set.
> >>>
> >>> If userspace then wants to take over the entry again,
> >>> br_fdb_external_learn_add() sees that BR_FDB_ADDED_BY_USER and skips
> >>> setting the BR_FDB_ADDED_BY_EXT_LEARN flags, thus silently ignores the
> >>> update:
> >>>
> >>> if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> >>> /* Refresh entry */
> >>> fdb->used = jiffies;
> >>> } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> >>> /* Take over SW learned entry */
> >>> set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
> >>> modified = true;
> >>> }
> >>>
> >>> Fix this by relaxing the condition for setting BR_FDB_ADDED_BY_EXT_LEARN
> >>> by also allowing it if swdev_notify is true, which it will only be for
> >>> user initiated updates.
> >>>
> >>> Fixes: 710ae7287737 ("net: bridge: Mark FDB entries that were added by user as such")
> >>> Signed-off-by: Jonas Gorski <jonas.gorski@...dn.de>
> >>> ---
> >>> net/bridge/br_fdb.c | 3 ++-
> >>> 1 file changed, 2 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> >>> index c77591e63841..c5d9ae13a6fb 100644
> >>> --- a/net/bridge/br_fdb.c
> >>> +++ b/net/bridge/br_fdb.c
> >>> @@ -1472,7 +1472,8 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
> >>> if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> >>> /* Refresh entry */
> >>> fdb->used = jiffies;
> >>> - } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> >>> + } else if (swdev_notify ||
> >>> + !test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> >>> /* Take over SW learned entry */
> >>> set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
> >>> modified = true;
> >>
> >> This literally means if added_by_user || !added_by_user, so you can probably
> >> rewrite that whole block to be more straight-forward with test_and_set_bit -
> >> if it was already set then refresh, if it wasn't modified = true
> >
> > Hi Nik,
> >
> > You mean like this [1]?
> > I deleted the comment about "SW learned entry" since "extern_learn" flag
> > not being set does not necessarily mean the entry was learned by SW.
> >
> > [1]
> > diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> > index c77591e63841..ad7a42b505ef 100644
> > --- a/net/bridge/br_fdb.c
> > +++ b/net/bridge/br_fdb.c
> > @@ -1469,12 +1469,10 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
> > modified = true;
> > }
> >
> > - if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> > + if (test_and_set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
> > /* Refresh entry */
> > fdb->used = jiffies;
> > - } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
> > - /* Take over SW learned entry */
> > - set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
> > + } else {
> > modified = true;
> > }
>
> Yeah, that's exactly what I meant. Since the added_by_user condition becomes
> redundant we can just drop it.
br_fdb_external_learn_add() is called from two places; once when
userspace adds a EXT_LEARN flagged fdb entry (then swdev_nofity is
set), and once when a switchdev driver reports it has learned an entry
(then swdev_notify isn't).
AFAIU the previous condition was to prevent user fdb entries from
being taken over by hardware / switchdev events, which this would now
allow to happen. OTOH, the switchdev notifications are a statement of
fact, and the kernel really has a say into whether the hardware should
keep the entry learned, so not allowing entries to be marked as
learned by hardware would also result in a disconnect between hardware
and kernel.
My change was trying to accomodate for the former one, i.e. if the
user bit is set, only the user may mark it as EXT_LEARN, but not any
(switchdev) drivers.
I have no strong feelings about what I think is right, so if this is
the wanted direction, I can send a V2 doing that.
Best Regards,
Jonas
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