linux-kernel - Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error

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Message-ID: <ab400cba7523e69b15360b0928cb8fa8b9432d86.camel@nokia.com>
Date:   Wed, 20 May 2020 15:42:17 +0000
From:   "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
To:     "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "dinghao.liu@....edu.cn" <dinghao.liu@....edu.cn>,
        "kjlu@....edu" <kjlu@....edu>
CC:     "mpm@...enic.com" <mpm@...enic.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "ben.dooks@...ethink.co.uk" <ben.dooks@...ethink.co.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "allison@...utok.net" <allison@...utok.net>,
        "yuehaibing@...wei.com" <yuehaibing@...wei.com>,
        "rfontana@...hat.com" <rfontana@...hat.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error

Hello Dinghao,

On Wed, 2020-05-20 at 21:29 +0800, Dinghao Liu wrote:
> pm_runtime_get_sync() increments the runtime PM usage counter even
> the call returns an error code. Thus a pairing decrement is needed
> on the error handling path to keep the counter balanced.

I believe, this is the wrong place for such kind of fix.
pm_runtime_get_sync() has obviously a broken semantics with regards to
your observation but no other driver does what you propose.
I think the proper fix belong into PM subsystem, please take a look
onto commit 15bcb91d7e60 "PM / Runtime: Implement autosuspend support".

> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  drivers/char/hw_random/ks-sa-rng.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/char/hw_random/ks-sa-rng.c b/drivers/char/hw_random/ks-sa-rng.c
> index e2330e757f1f..85c81da4a8af 100644
> --- a/drivers/char/hw_random/ks-sa-rng.c
> +++ b/drivers/char/hw_random/ks-sa-rng.c
> @@ -244,6 +244,7 @@ static int ks_sa_rng_probe(struct platform_device *pdev)
>  	ret = pm_runtime_get_sync(dev);
>  	if (ret < 0) {
>  		dev_err(dev, "Failed to enable SA power-domain\n");
> +		pm_runtime_put_sync(dev);
>  		pm_runtime_disable(dev);
>  		return ret;
>  	}
-- 
Alexander Sverdlin.