linux-kernel - Re: [PATCH] iommu/vt-d: Fix an unbalanced rcu_read_lock/rcu_read

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Message-ID: <c7ac5f27-d7b6-6f19-75cc-c047ad590696@linux.intel.com>
Date:   Mon, 8 Nov 2021 10:18:17 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        dwmw2@...radead.org, joro@...tes.org, will@...nel.org,
        kevin.tian@...el.com
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Fix an unbalanced
 rcu_read_lock/rcu_read_unlock()

On 11/7/21 12:53 AM, Christophe JAILLET wrote:
> If we return -EOPNOTSUPP, the rcu lock remains lock. This is spurious.
> Go through the end of the function instead. This way, the missing
> 'rcu_read_unlock()' is called.
> 
> Fixes: 7afd7f6aa21a ("iommu/vt-d: Check FL and SL capability sanity in scalable mode")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> This patch is speculative, review with care.
> ---
>   drivers/iommu/intel/cap_audit.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel/cap_audit.c b/drivers/iommu/intel/cap_audit.c
> index b39d223926a4..71596fc62822 100644
> --- a/drivers/iommu/intel/cap_audit.c
> +++ b/drivers/iommu/intel/cap_audit.c
> @@ -144,6 +144,7 @@ static int cap_audit_static(struct intel_iommu *iommu, enum cap_audit_type type)
>   {
>   	struct dmar_drhd_unit *d;
>   	struct intel_iommu *i;
> +	int rc = 0;
>   
>   	rcu_read_lock();
>   	if (list_empty(&dmar_drhd_units))
> @@ -169,11 +170,11 @@ static int cap_audit_static(struct intel_iommu *iommu, enum cap_audit_type type)
>   	 */
>   	if (intel_cap_smts_sanity() &&
>   	    !intel_cap_flts_sanity() && !intel_cap_slts_sanity())
> -		return -EOPNOTSUPP;
> +		rc = -EOPNOTSUPP;
>   
>   out:
>   	rcu_read_unlock();
> -	return 0;
> +	return rc;
>   }
>   
>   int intel_cap_audit(enum cap_audit_type type, struct intel_iommu *iommu)
> 

Nice catch! Thank you!

I will queue this for v5.16.

Best regards,
baolu