linux-kernel - Re: [PATCH net V2 2/4] net/mlx5: Fix deadlock between devlink lock and esw->wq

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Message-ID: <20260202162948.4e743216@kernel.org>
Date: Mon, 2 Feb 2026 16:29:48 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Cosmin Ratiu <cratiu@...dia.com>
Cc: "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
 "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
 "davem@...emloft.net" <davem@...emloft.net>, Tariq Toukan
 <tariqt@...dia.com>, Gal Pressman <gal@...dia.com>, Mark Bloch
 <mbloch@...dia.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, Moshe Shemesh <moshe@...dia.com>,
 "pabeni@...hat.com" <pabeni@...hat.com>, "edumazet@...gle.com"
 <edumazet@...gle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 Saeed Mahameed <saeedm@...dia.com>, "leon@...nel.org" <leon@...nel.org>,
 "horms@...nel.org" <horms@...nel.org>
Subject: Re: [PATCH net V2 2/4] net/mlx5: Fix deadlock between devlink lock
 and esw->wq

On Mon, 2 Feb 2026 14:48:28 +0000 Cosmin Ratiu wrote:
> > And having a refount on (I presume) struct mlx5_esw_functions
> > so that work can hold a ref is not an option?
> > Are you planning to revisit this in -next?  
> 
> Currently, mlx5_eswitch_disable_locked (with the devlink lock held)
> waits for esw_vfs_changed_event_handler to finish.
> The event handler needs to acquire the same lock and load/unload all
> VFs, which touches the entire esw.
> I don't currently see how to use reference counting on the esw to avoid
> waiting for the handler.

struct my_thing_with_work {
	work;
	refcount;
	dead;
};

work() {
	lock()
	if (my_thing->dead)
		goto out;
	/* .. add code here .. */
out:
	unlock()
	my_thing_put(my_thing)
}

some_op() {
	// assuming lock() held
	if (!work_queued(my_thing->work)) {
		refcount_inc(my_thing->refcount);
		queue_work(my_thing->work)
	}
}

shutdown_op() {
	// assuming lock() held
	if (cancel_work())
		my_thing_put(my_thing)

	my_thing->dead = true;
	my_thing_put(my_thing)
}