linux-kernel - Re: [PATCH 0/9] net: bridge: reduce multicast checks in fast path

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Message-ID: <20250829084747.55c6386f@kernel.org>
Date: Fri, 29 Aug 2025 08:47:47 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Linus Lüssing <linus.luessing@...3.blue>
Cc: bridge@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Nikolay Aleksandrov <razor@...ckwall.org>,
 Ido Schimmel <idosch@...dia.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 Simon Horman <horms@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Eric
 Dumazet <edumazet@...gle.com>, "David S . Miller" <davem@...emloft.net>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Stanislav Fomichev
 <sdf@...ichev.me>, Xiao Liang <shaw.leon@...il.com>
Subject: Re: [PATCH 0/9] net: bridge: reduce multicast checks in fast path

On Fri, 29 Aug 2025 10:53:41 +0200 Linus Lüssing wrote:
> This patchset introduces new state variables to combine and reduce the
> number of checks we would otherwise perform on every multicast packet
> in fast/data path.
>   
> The second reason for introducing these new, internal multicast active
> variables is to later propagate a safety mechanism which was introduced
> in b00589af3b04 ("bridge: disable snooping if there is no querier") to
> switchdev/DSA, too. That is to notify switchdev/DSA if multicast
> snooping can safely be applied without potential packet loss.

Please leave the git-generated diff stat in the cover letter.
Please include tree designation in the subject, per:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html

I'll leave the real review to the experts but this series appears
to make kselftests unhappy:

[  106.423894] WARNING: CPU: 3 PID: 1121 at net/bridge/br_multicast.c:1388 __br_multicast_stop+0xa0/0xc0 [bridge]
[  106.424022] Modules linked in: sch_ingress 8021q act_mirred cls_matchall sch_red dummy bridge stp llc sch_tbf vrf veth
[  106.424144] CPU: 3 UID: 0 PID: 1121 Comm: ip Not tainted 6.17.0-rc2-virtme #1 PREEMPT(voluntary) 
[  106.424235] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[  106.424301] RIP: 0010:__br_multicast_stop+0xa0/0xc0 [bridge]
[  106.424371] Code: 89 df e8 f3 fd ff ff 80 bb 2c 01 00 00 00 75 19 80 bb 0c 02 00 00 00 75 1d 48 8b 3b 5b 48 81 c7 4c 03 00 00 e9 b1 c2 0b f8 90 <0f> 0b 90 80 bb 0c 02 00 00 00 74 e3 90 0f 0b 90 48 8b 3b 5b 48 81
[  106.424544] RSP: 0018:ffffb78500283888 EFLAGS: 00010202
[  106.424586] RAX: 0000000000000000 RBX: ffff979907d81af0 RCX: 0000000000000000
[  106.424665] RDX: ffff979907d81c50 RSI: 0000000000000001 RDI: ffff979907d819c0
[  106.424753] RBP: ffff979907d819c0 R08: ffffffffb94f0180 R09: ffffb78500283b40
[  106.424836] R10: ffff97990342d250 R11: ffff979907d81000 R12: ffff979907d819c0
[  106.424913] R13: 0000000000000002 R14: 0000000000000001 R15: 0000000000000001
[  106.424992] FS:  00007f7e9de78800(0000) GS:ffff979985967000(0000) knlGS:0000000000000000
[  106.425073] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  106.425144] CR2: 0000000000447b60 CR3: 0000000004d3b003 CR4: 0000000000772ef0
[  106.425226] PKRU: 55555554
[  106.425250] Call Trace:
[  106.425278]  <TASK>
[  106.425305]  br_multicast_toggle_vlan_snooping+0x1a9/0x1e0 [bridge]
[  106.425383]  br_boolopt_multi_toggle+0x54/0x90 [bridge]
[  106.425443]  br_changelink+0x4be/0x510 [bridge]
[  106.425510]  ? ns_capable+0x2d/0x60
[  106.425557]  rtnl_newlink+0x73f/0xbc0
[  106.425605]  ? rtnl_setlink+0x2c0/0x2c0
[  106.425633]  rtnetlink_rcv_msg+0x358/0x400
[  106.425676]  ? update_load_avg+0x6f/0x350
[  106.425726]  ? rtnl_calcit.isra.0+0x110/0x110
[  106.425778]  netlink_rcv_skb+0x57/0x100
[  106.425819]  netlink_unicast+0x252/0x380
[  106.425858]  ? __alloc_skb+0xdb/0x190
[  106.425904]  netlink_sendmsg+0x1be/0x3e0
[  106.425945]  ____sys_sendmsg+0x132/0x260
[  106.425984]  ? copy_msghdr_from_user+0x6c/0xa0
[  106.426039]  ___sys_sendmsg+0x87/0xd0
[  106.426083]  ? __handle_mm_fault+0xa41/0xe50
[  106.426144]  __sys_sendmsg+0x71/0xd0
[  106.426184]  do_syscall_64+0xa4/0x260
[  106.426224]  entry_SYSCALL_64_after_hwframe+0x4b/0x53
[  106.426279] RIP: 0033:0x7f7e9e0451e7