linux-kernel - Re: [PATCH v1] Moving init_completion before request

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Date:   Fri, 29 Jul 2022 12:21:31 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Kshitiz Varshney <kshitiz.varshney@....com>,
        Horia Geanta <horia.geanta@....com>,
        Pankaj Gupta <pankaj.gupta@....com>,
        Varun Sethi <V.Sethi@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Iuliana Prodan <iuliana.prodan@....com>,
        Gaurav Jain <gaurav.jain@....com>,
        Rahul Kumar Yadav <rahulkumar.yadav@....com>,
        Vabhav Sharma <vabhav.sharma@....com>,
        Sahil Malhotra <sahil.malhotra@....com>,
        Matt Mackall <mpm@...enic.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        Martin Kaiser <martin@...ser.cx>
Cc:     linux-imx@....com, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] Moving init_completion before request_irq

Hello Kshitiz,

On 29.07.22 12:02, Kshitiz Varshney wrote:
> Issue:
> While servicing interrupt, trying to access variable rng_op_done,
> which is not yet initalized hence causing kernel to crash
> while booting.
> 
> Fix:
> Moving initialization of rng_op_done before request_irq.
> 
> Fixes: 1d5449445bd0 (hwrng: mx-rngc - add a driver for Freescale RNGC)
> Signed-off-by: Kshitiz Varshney <kshitiz.varshney@....com>

Thanks for your patch.

> +	init_completion(&rngc->rng_op_done);
> +
>  	ret = devm_request_irq(&pdev->dev,
>  			irq, imx_rngc_irq, 0, pdev->name, (void *)rngc);

This should probably be moved below imx_rngc_irq_mask_clear(rngc).
init_completion can stay where it is. That way:

 - You initialize rngc fully before registering the IRQ handler
 - You don't handle pending IRQs that you want to dismiss anyway
 - If the IRQ happens to be because of a SEED_DONE due to a previous
   boot stage, you don't end up completing the completion prematurely.

Cheers,
Ahmad

>  	if (ret) {
> @@ -277,7 +279,6 @@ static int imx_rngc_probe(struct platform_device *pdev)
>  		goto err;
>  	}
>  
> -	init_completion(&rngc->rng_op_done);
>  
>  	rngc->rng.name = pdev->name;
>  	rngc->rng.init = imx_rngc_init;


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