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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Marc Zyngier <maz@kernel.org>, linux-kernel@vger.kernel.org
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Ley Foon Tan <ley.foon.tan@intel.com>,
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        Max Filippov <jcmvbkbc@gmail.com>,
        Vineet Gupta <vgupta@synopsys.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Robert Jarzmik <robert.jarzmik@free.fr>,
        Russell King <linux@armlinux.org.uk>,
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        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
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        Christian =?utf-8?Q?K=C3=B6nig?= <christian.koenig@amd.com>,
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        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
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        Bjorn Helgaas <bhelgaas@google.com>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        kernel-team@android.com
Subject: Re: [PATCH 20/39] irqdomain: Protect the linear revmap with RCU
In-Reply-To: <20210520163751.27325-21-maz@kernel.org>
References: <20210520163751.27325-1-maz@kernel.org> <20210520163751.27325-21-maz@kernel.org>
Date:   Sat, 19 Jun 2021 13:37:33 +0200
Message-ID: <87zgvmccg2.ffs@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Thu, May 20 2021 at 17:37, Marc Zyngier wrote:
>  static void irq_domain_clear_mapping(struct irq_domain *domain,
> @@ -902,12 +901,12 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
>  		return 0;
>  	}
>  
> +	rcu_read_lock();
>  	/* Check if the hwirq is in the linear revmap. */
>  	if (hwirq < domain->revmap_size)
> -		return domain->revmap[hwirq]->irq;
> -
> -	rcu_read_lock();
> -	data = radix_tree_lookup(&domain->revmap_tree, hwirq);
> +		data = rcu_dereference(domain->revmap[hwirq]);
> +	else
> +		data = radix_tree_lookup(&domain->revmap_tree, hwirq);
>  	rcu_read_unlock();
>  	return data ? data->irq : 0;

This is wrong and was wrong before. This wants to be:

     irq = data ? data->irq : 0;
     rcu_read_unlock();
     return irq;

Thanks,

        tglx