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

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Message-ID: <aLd2_um-oWhS23Md@sellars>
Date: Wed, 3 Sep 2025 01:00:14 +0200
From: Linus Lüssing <linus.luessing@...3.blue>
To: Nikolay Aleksandrov <razor@...ckwall.org>
Cc: Jakub Kicinski <kuba@...nel.org>, bridge@...ts.linux.dev,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.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 Tue, Sep 02, 2025 at 10:16:04PM +0200, Linus Lüssing wrote:
> On the other hand, moving the spinlock out of / around
> __br_multicast_stop() would lead to a sleeping-while-atomic bug
> when calling timer_delete_sync() in there. And if I were to change
> these to a timer_delete() I guess there is no way to do the sync
> part after unlocking? There is no equivalent to something like the
> flush_workqueue() / drain_workqueue() for workqueues, but for
> simple timers instead, right?

I'm wondering if it would be sufficient to use timer_del() on
.ndo_stop->br_dev_stop()->br_multicast_stop().

And use timer_del_sync() only on
.ndo_uninit->br_dev_uninit()-> br_multicast_dev_del()->
br_multicast_ctx_deinit() and
br_vlan_put_master()->br_multicast_ctx_deinit().


So basically only sync / wait for timer callbacks to finish if
their context is about to be free'd, on bridge or VLAN destruction?