Hi Joerg,
On Thu, Jun 18, 2015 at 10:50:20AM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@xxxxxxx>
>
> The use of the SR-IOV lock for ATS causes a dead-lock in the
> AMD-IOMMU driver when virtual functions are added that have
> an ATS capability.
>
> The problem is that the VFs will be added to the bus with
> the SR-IOV lock held. While added to the bus the
> device-notifiers will run and invoke AMD IOMMU code, which
> itself will assign the device to a domain try to enable ATS.
> When it calls pci_enable_ats() this will dead-lock.
I'm trying to connect the dots here. What's the notifier that invokes the
AMD IOMMU code? I thought it would be a BUS_NOTIFY_ADD_DEVICE notifier,
but I haven't found it yet.
> Fix this by introducing a global ats_lock. ATS enablement
> and disablement isn't in any fast-path, so a global lock
> shouldn't hurt here.
>
> Cc: stable@xxxxxxxxxx
> Reported-by: Gregor Dick <gdick@xxxxxxxxxxxxxx>
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
> drivers/pci/ats.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index a8099d4..f0c3c6f 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -17,6 +17,8 @@
>
> #include "pci.h"
>
> +static DEFINE_MUTEX(ats_lock);
> +
> static int ats_alloc_one(struct pci_dev *dev, int ps)
> {
> int pos;
> @@ -67,7 +69,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
> if (dev->is_physfn || dev->is_virtfn) {
> struct pci_dev *pdev = dev->is_physfn ? dev : dev->physfn;
>
> - mutex_lock(&pdev->sriov->lock);
> + mutex_lock(&ats_lock);
> if (pdev->ats)
> rc = pdev->ats->stu == ps ? 0 : -EINVAL;
> else
> @@ -75,7 +77,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
>
> if (!rc)
> pdev->ats->ref_cnt++;
> - mutex_unlock(&pdev->sriov->lock);
> + mutex_unlock(&ats_lock);
The mutex was originally added by e277d2fc79d6 ("PCI: handle Virtual
Function ATS enabling"). I assume the purpose is to protect the
ats_alloc_one().
This seems overly complicated. I think we can simplify this by doing some
of this work earlier, in pci_init_capabilities(). I'll work this up and
you can see what you think.
Bjorn
> if (rc)
> return rc;
> }
> @@ -116,11 +118,11 @@ void pci_disable_ats(struct pci_dev *dev)
> if (dev->is_physfn || dev->is_virtfn) {
> struct pci_dev *pdev = dev->is_physfn ? dev : dev->physfn;
>
> - mutex_lock(&pdev->sriov->lock);
> + mutex_lock(&ats_lock);
> pdev->ats->ref_cnt--;
> if (!pdev->ats->ref_cnt)
> ats_free_one(pdev);
> - mutex_unlock(&pdev->sriov->lock);
> + mutex_unlock(&ats_lock);
> }
>
> if (!dev->is_physfn)
> --
> 1.9.1
>
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