> From: Lu Baolu <baolu...@linux.intel.com>
> Sent: Tuesday, June 14, 2022 10:52 AM
>
> The device_domain_lock is used to protect the device tracking list of
> a domain. Remove unnecessary spin_lock/unlock()'s and move the necessary
> ones around the list access.
>
> Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
> ---
> drivers/iommu/intel/iommu.c | 68 +++++++++++++++----------------------
> 1 file changed, 27 insertions(+), 41 deletions(-)
>
[...]
> +iommu_support_dev_iotlb(struct dmar_domain *domain, struct
> intel_iommu *iommu,
> + u8 bus, u8 devfn)
> {
> - struct device_domain_info *info;
> -
> - assert_spin_locked(&device_domain_lock);
> + struct device_domain_info *info = NULL, *tmp;
> + unsigned long flags;
>
> if (!iommu->qi)
> return NULL;
>
> - list_for_each_entry(info, &domain->devices, link)
> - if (info->iommu == iommu && info->bus == bus &&
> - info->devfn == devfn) {
> - if (info->ats_supported && info->dev)
> - return info;
> + spin_lock_irqsave(&device_domain_lock, flags);
> + list_for_each_entry(tmp, &domain->devices, link) {
> + if (tmp->iommu == iommu && tmp->bus == bus &&
> + tmp->devfn == devfn) {
> + if (tmp->ats_supported)
> + info = tmp;
Directly returning with unlock here is clearer than adding
another tmp variable...
> @@ -2460,15 +2450,14 @@ static int domain_add_dev_info(struct
> dmar_domain *domain, struct device *dev)
> if (!iommu)
> return -ENODEV;
>
> - spin_lock_irqsave(&device_domain_lock, flags);
> - info->domain = domain;
> ret = domain_attach_iommu(domain, iommu);
> - if (ret) {
> - spin_unlock_irqrestore(&device_domain_lock, flags);
> + if (ret)
> return ret;
> - }
> +
> + spin_lock_irqsave(&device_domain_lock, flags);
> list_add(&info->link, &domain->devices);
> spin_unlock_irqrestore(&device_domain_lock, flags);
> + info->domain = domain;
>
This is incorrect. You need fully initialize the object before adding
it to the list. Otherwise a search right after above unlock and
before assigning info->domain will get a wrong data
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