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SubjectRe: [PATCH 23/34] AMD IOMMU: add functions to find IOMMU device resources
On Thu, 26 Jun 2008 21:27:59 +0200 Joerg Roedel <joerg.roedel@amd.com> wrote:

> This patch adds functions necessary to find the IOMMU resources for a specific
> device.
>
> Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
> ---
> arch/x86/kernel/amd_iommu.c | 75 +++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 75 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
> index c43d15d..47e80b5 100644
> --- a/arch/x86/kernel/amd_iommu.c
> +++ b/arch/x86/kernel/amd_iommu.c
> @@ -461,3 +461,78 @@ free_dma_dom:
> return NULL;
> }
>
> +static struct protection_domain *domain_for_device(u16 devid)
> +{
> + struct protection_domain *dom;
> + unsigned long flags;
> +
> + read_lock_irqsave(&amd_iommu_devtable_lock, flags);

Why is this cheerfully undocumented lock irq-safe? Is it ever taken from
IRQ context?

> + dom = amd_iommu_pd_table[devid];
> + read_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
> +
> + return dom;
> +}

The locking in this function makes no sense. We drop the lock then return
a value which the caller cannot use in a race-free fashion, because the
lock is no longer held.




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