linux-kernel - Re: [PATCH] net/802/garp: fix potential deadlock on &app->lock

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Message-ID: <CANn89iJRaT1B=HwWDsEdcAUZzYERzeR8iwGYHZuLcy+G4G39Lw@mail.gmail.com>
Date:   Tue, 27 Jun 2023 15:55:11 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/802/garp: fix potential deadlock on &app->lock

On Tue, Jun 27, 2023 at 12:52 PM Chengfeng Ye <dg573847474@...il.com> wrote:
>
> As &app->lock is also acquired by the timer garp_join_timer() which
> which executes under soft-irq context, code executing under process
> context should disable irq before acquiring the lock, otherwise
> deadlock could happen if the process context hold the lock then
> preempt by the interruption.
>
> garp_pdu_rcv() is one such function that acquires &app->lock, but I
> am not sure whether it is called with irq disable outside thus the
> patch could be false.
>
> Possible deadlock scenario:
> garp_pdu_rcv()
>     -> spin_lock(&app->lock)
>         <timer interrupt>

This can not happen.

RX handlers are called from BH context, and rcu_read_lock()

See net/core/dev.c,  deliver_skb() and netif_receive_skb()


>         -> garp_join_timer()
>         -> spin_lock(&app->lock)
>
> This flaw was found using an experimental static analysis tool we are
> developing for irq-related deadlock.
>
> The tentative patch fix the potential deadlock by spin_lock_irqsave(),
> or it should be fixed with spin_lock_bh() if it is a real bug? I am
> not very sure.

I guess more work is needed at your side :)