linux-kernel - Re: [PATCH] iommu/arm-smmu: Fix arm_smmu_device refcount leak when arm_smmu_rpm

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Date:   Wed, 9 Jun 2021 15:12:11 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>, Will Deacon <will@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krishna Reddy <vdumpa@...dia.com>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] iommu/arm-smmu: Fix arm_smmu_device refcount leak when
 arm_smmu_rpm_get fails

On 2021-06-09 14:35, Xiyu Yang wrote:
> arm_smmu_rpm_get() invokes pm_runtime_get_sync(), which increases the
> refcount of the "smmu" even though the return value is less than 0.
> 
> The reference counting issue happens in some error handling paths of
> arm_smmu_rpm_get() in its caller functions. When arm_smmu_rpm_get()
> fails, the caller functions forget to decrease the refcount of "smmu"
> increased by arm_smmu_rpm_get(), causing a refcount leak.
> 
> Fix this issue by calling arm_smmu_rpm_put() or jumping to the "rpm_put"
> label when arm_smmu_rpm_get() fails.

If only there was some kind of helper function which could encapsulate 
the correct expected behaviour in a single place...

In fact with the new pm_runtime_resume_and_get() API I think these two 
patches boil down to a one-line change.

Thanks,
Robin.

> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> ---
>   drivers/iommu/arm/arm-smmu/arm-smmu.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index 6f72c4d208ca..177ee54c5534 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -840,7 +840,7 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>   
>   	ret = arm_smmu_rpm_get(smmu);
>   	if (ret < 0)
> -		return;
> +		goto rpm_put;
>   
>   	/*
>   	 * Disable the context bank and free the page tables before freeing
> @@ -857,6 +857,7 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>   	free_io_pgtable_ops(smmu_domain->pgtbl_ops);
>   	__arm_smmu_free_bitmap(smmu->context_map, cfg->cbndx);
>   
> +rpm_put:
>   	arm_smmu_rpm_put(smmu);
>   }
>   
> @@ -1153,7 +1154,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   
>   	ret = arm_smmu_rpm_get(smmu);
>   	if (ret < 0)
> -		return ret;
> +		goto rpm_put;
>   
>   	/* Ensure that the domain is finalised */
>   	ret = arm_smmu_init_domain_context(domain, smmu, dev);
> @@ -1404,7 +1405,7 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
>   
>   	ret = arm_smmu_rpm_get(smmu);
>   	if (ret < 0)
> -		goto out_cfg_free;
> +		goto rpm_put;
>   
>   	ret = arm_smmu_master_alloc_smes(dev);
>   	arm_smmu_rpm_put(smmu);
> @@ -1417,6 +1418,8 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
>   
>   	return &smmu->iommu;
>   
> +rpm_put:
> +	arm_smmu_rpm_put(smmu);
>   out_cfg_free:
>   	kfree(cfg);
>   out_free:
> @@ -1438,8 +1441,10 @@ static void arm_smmu_release_device(struct device *dev)
>   	smmu = cfg->smmu;
>   
>   	ret = arm_smmu_rpm_get(smmu);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		arm_smmu_rpm_put(smmu);
>   		return;
> +	}
>   
>   	arm_smmu_master_free_smes(cfg, fwspec);
>   
>