linux-kernel - Re: [PATCH net v3] netconsole: Fix race condition in between reader and writer of userdata

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Message-ID: <CAGSyskVvHvK3R0SQ+yg3050E_btovVY8L2iQ1gUvJ2GigKa5iw@mail.gmail.com>
Date: Tue, 28 Oct 2025 21:28:42 +0000
From: Gustavo Luiz Duarte <gustavold@...il.com>
To: Andre Carvalho <asantostc@...il.com>, Simon Horman <horms@...nel.org>, 
	Breno Leitao <leitao@...ian.org>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Matthew Wood <thepacketgeek@...il.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3] netconsole: Fix race condition in between reader
 and writer of userdata

On Mon, Oct 27, 2025 at 4:08 PM Gustavo Luiz Duarte <gustavold@...il.com> wrote:
> @@ -888,6 +888,9 @@ static void update_userdata(struct netconsole_target *nt)
>  {
>         int complete_idx = 0, child_count = 0;
>         struct list_head *entry;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&target_list_lock, flags);

I realize that we might call WARN_ON_ONCE() while holding this
spinlock, which could deadlock trying to write to netconsole.
Let me send v4 addressing that.