linux-kernel - Re: [PATCH 02/23] interconnect: fix icc_provider

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Date:   Wed, 1 Feb 2023 12:16:50 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Johan Hovold <johan+linaro@...nel.org>,
        Georgi Djakov <djakov@...nel.org>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Artur Świgoń <a.swigon@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 02/23] interconnect: fix icc_provider_del() error handling



On 1.02.2023 11:15, Johan Hovold wrote:
> The interconnect framework currently expects that providers are only
> removed when there are no users and after all nodes have been removed.
> 
> There is currently nothing that guarantees this to be the case and the
> framework does not do any reference counting, but refusing to remove the
> provider is never correct as that would leave a dangling pointer to a
> resource that is about to be released in the global provider list (e.g.
> accessible through debugfs).
> 
> Replace the current sanity checks with WARN_ON() so that the provider is
> always removed.
I spent a considerable amount of time scratching my head what WARN_ON has
to do with removing list items.. I suppose "don't return early and replace
pr_warn with WARN_ON" would have been clearer, but maybe that's just me
in the morning..

> 
> Fixes: 11f1ceca7031 ("interconnect: Add generic on-chip interconnect API")
> Cc: stable@...r.kernel.org      # 5.1: 680f8666baf6: interconnect: Make icc_provider_del() return void
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
Reviewed-by: Konrad Dybcio <konrad.dybcio@...aro.org>

Konrad
>  drivers/interconnect/core.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
> index dc61620a0191..43c5c8503ee8 100644
> --- a/drivers/interconnect/core.c
> +++ b/drivers/interconnect/core.c
> @@ -1062,18 +1062,8 @@ EXPORT_SYMBOL_GPL(icc_provider_add);
>  void icc_provider_del(struct icc_provider *provider)
>  {
>  	mutex_lock(&icc_lock);
> -	if (provider->users) {
> -		pr_warn("interconnect provider still has %d users\n",
> -			provider->users);
> -		mutex_unlock(&icc_lock);
> -		return;
> -	}
> -
> -	if (!list_empty(&provider->nodes)) {
> -		pr_warn("interconnect provider still has nodes\n");
> -		mutex_unlock(&icc_lock);
> -		return;
> -	}
> +	WARN_ON(provider->users);
> +	WARN_ON(!list_empty(&provider->nodes));
>  
>  	list_del(&provider->provider_list);
>  	mutex_unlock(&icc_lock);