From:   Thomas Gleixner <tglx@linutronix.de>
To:     Shanker Donthineni <sdonthineni@nvidia.com>,
        Marc Zyngier <maz@kernel.org>, Michael Walle <michael@walle.cc>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Hans de Goede <hdegoede@redhat.com>,
        Wolfram Sang <wsa+renesas@sang-engineering.com>,
        Shanker Donthineni <sdonthineni@nvidia.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] genirq: Use hlist for managing resend handlers
In-Reply-To: <20230130005725.3517597-2-sdonthineni@nvidia.com>
References: <20230130005725.3517597-1-sdonthineni@nvidia.com>
 <20230130005725.3517597-2-sdonthineni@nvidia.com>
Date:   Tue, 31 Jan 2023 09:59:37 +0100
Message-ID: <87pmav13ly.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Sun, Jan 29 2023 at 18:57, Shanker Donthineni wrote:
> +/* hlist_head to handle software resend of interrupts: */
> +static HLIST_HEAD(irq_resend_list);
> +static DEFINE_RAW_SPINLOCK(irq_resend_lock);
>  
>  /*
>   * Run software resends of IRQ's
> @@ -30,18 +31,16 @@ static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
>  static void resend_irqs(struct tasklet_struct *unused)
>  {
>  	struct irq_desc *desc;
> -	int irq;
> -
> -	while (!bitmap_empty(irqs_resend, nr_irqs)) {
> -		irq = find_first_bit(irqs_resend, nr_irqs);
> -		clear_bit(irq, irqs_resend);
> -		desc = irq_to_desc(irq);
> -		if (!desc)
> -			continue;
> +	struct hlist_node *n;
> +
> +	raw_spin_lock_irq(&irq_resend_lock);
> +	hlist_for_each_entry_safe(desc, n, &irq_resend_list, resend_node) {
> +		hlist_del_init(&desc->resend_node);
>  		local_irq_disable();
>  		desc->handle_irq(desc);
>  		local_irq_enable();
>  	}
> +	raw_spin_unlock_irq(&irq_resend_lock);

The lock ordering is broken here. irq_sw_resend() is invoked with
desc->lock held and takes irq_resend_lock.

Lockdep clearly would have told you...

	raw_spin_lock_irq(&irq_resend_lock);
        while (!hlist_empty(...)) {
        	desc = hlist_entry(irq_resend_list.first, ...);
		hlist_del_init(&desc->resend_node);
                raw_spin_unlock(&...);
                desc->handle_irq();
                raw_spin_lock(&...);
        }        

Hmm?

Thanks,

        tglx