Re: [RFC PATCH v1 01/22] PCI: use pci_get_domain_bus_and_slot() toavoid race conditions

[Bjorn Helgaas]

On Tue, Aug 7, 2012 at 10:10 AM, Jiang Liu <liuj97@xxxxxxxxx> wrote:
> There's a typical usage pattern to search a PCI device under a specific
> PCI bus (domian, busno) as below:
> struct pci_bus *pci_bus = pci_find_bus(domain, busno);
> struct pci_dev *pci_dev = pci_get_slot(pci_bus, devfn);
>
> The above code has a race window between pci_find_bus() and pci_get_slot()
> if PCI hotplug operations happen between them which removes the pci_bus.
> So use PCI hotplug safe interface pci_get_domain_bus_and_slot() instead,
> which also reduces code complexity.

This makes sense to me.  If we support hotplug, it's fundamentally
unsafe to keep a struct pci_bus * without having a reference or some
way to make sure it doesn't go away.  I think we should try to
eradicate all uses of pci_find_bus() and pci_find_next_bus().

> Signed-off-by: Jiang Liu <liuj97@xxxxxxxxx>
> ---
>  arch/ia64/sn/kernel/io_common.c      |    4 +---
>  drivers/gpu/vga/vgaarb.c             |   15 +++------------
>  drivers/pci/hotplug/cpcihp_generic.c |    8 ++------
>  drivers/pci/iov.c                    |    8 ++------
>  drivers/pci/xen-pcifront.c           |   10 ++--------
>  5 files changed, 10 insertions(+), 35 deletions(-)
>
> diff --git a/arch/ia64/sn/kernel/io_common.c b/arch/ia64/sn/kernel/io_common.c
> index fbb5f2f..8630875 100644
> --- a/arch/ia64/sn/kernel/io_common.c
> +++ b/arch/ia64/sn/kernel/io_common.c
> @@ -229,7 +229,6 @@ void sn_pci_fixup_slot(struct pci_dev *dev, struct pcidev_info *pcidev_info,
>  {
>         int segment = pci_domain_nr(dev->bus);
>         struct pcibus_bussoft *bs;
> -       struct pci_bus *host_pci_bus;
>         struct pci_dev *host_pci_dev;
>         unsigned int bus_no, devfn;
>
> @@ -245,8 +244,7 @@ void sn_pci_fixup_slot(struct pci_dev *dev, struct pcidev_info *pcidev_info,
>
>         bus_no = (pcidev_info->pdi_slot_host_handle >> 32) & 0xff;
>         devfn = pcidev_info->pdi_slot_host_handle & 0xffffffff;
> -       host_pci_bus = pci_find_bus(segment, bus_no);
> -       host_pci_dev = pci_get_slot(host_pci_bus, devfn);
> +       host_pci_dev = pci_get_domain_bus_and_slot(segment, bus_no, devfn);
>
>         pcidev_info->host_pci_dev = host_pci_dev;
>         pcidev_info->pdi_linux_pcidev = dev;
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 3df8fc0..b6852b7 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -1066,7 +1066,6 @@ static ssize_t vga_arb_write(struct file *file, const char __user * buf,
>                 }
>
>         } else if (strncmp(curr_pos, "target ", 7) == 0) {
> -               struct pci_bus *pbus;
>                 unsigned int domain, bus, devfn;
>                 struct vga_device *vgadev;
>
> @@ -1085,19 +1084,11 @@ static ssize_t vga_arb_write(struct file *file, const char __user * buf,
>                         pr_debug("vgaarb: %s ==> %x:%x:%x.%x\n", curr_pos,
>                                 domain, bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
>
> -                       pbus = pci_find_bus(domain, bus);
> -                       pr_debug("vgaarb: pbus %p\n", pbus);
> -                       if (pbus == NULL) {
> -                               pr_err("vgaarb: invalid PCI domain and/or bus address %x:%x\n",
> -                                       domain, bus);
> -                               ret_val = -ENODEV;
> -                               goto done;
> -                       }
> -                       pdev = pci_get_slot(pbus, devfn);
> +                       pdev = pci_get_domain_bus_and_slot(domain, bus, devfn);
>                         pr_debug("vgaarb: pdev %p\n", pdev);
>                         if (!pdev) {
> -                               pr_err("vgaarb: invalid PCI address %x:%x\n",
> -                                       bus, devfn);
> +                               pr_err("vgaarb: invalid PCI address %x:%x:%x\n",
> +                                       domain, bus, devfn);
>                                 ret_val = -ENODEV;
>                                 goto done;
>                         }
> diff --git a/drivers/pci/hotplug/cpcihp_generic.c b/drivers/pci/hotplug/cpcihp_generic.c
> index 81af764..a6a71c4 100644
> --- a/drivers/pci/hotplug/cpcihp_generic.c
> +++ b/drivers/pci/hotplug/cpcihp_generic.c
> @@ -154,12 +154,8 @@ static int __init cpcihp_generic_init(void)
>         if(!r)
>                 return -EBUSY;
>
> -       bus = pci_find_bus(0, bridge_busnr);
> -       if (!bus) {
> -               err("Invalid bus number %d", bridge_busnr);
> -               return -EINVAL;
> -       }
> -       dev = pci_get_slot(bus, PCI_DEVFN(bridge_slot, 0));
> +       dev = pci_get_domain_bus_and_slot(0, bridge_busnr,
> +                                         PCI_DEVFN(bridge_slot, 0));
>         if(!dev || dev->hdr_type != PCI_HEADER_TYPE_BRIDGE) {
>                 err("Invalid bridge device %s", bridge);
>                 pci_dev_put(dev);
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 74bbaf8..c7d2969 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -152,15 +152,11 @@ failed1:
>  static void virtfn_remove(struct pci_dev *dev, int id, int reset)
>  {
>         char buf[VIRTFN_ID_LEN];
> -       struct pci_bus *bus;
>         struct pci_dev *virtfn;
>         struct pci_sriov *iov = dev->sriov;
>
> -       bus = pci_find_bus(pci_domain_nr(dev->bus), virtfn_bus(dev, id));
> -       if (!bus)
> -               return;
> -
> -       virtfn = pci_get_slot(bus, virtfn_devfn(dev, id));
> +       virtfn = pci_get_domain_bus_and_slot(pci_domain_nr(dev->bus),
> +                       virtfn_bus(dev, id), virtfn_devfn(dev, id));
>         if (!virtfn)
>                 return;
>
> diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
> index d6cc62c..def8d0b 100644
> --- a/drivers/pci/xen-pcifront.c
> +++ b/drivers/pci/xen-pcifront.c
> @@ -982,7 +982,6 @@ static int pcifront_detach_devices(struct pcifront_device *pdev)
>         int err = 0;
>         int i, num_devs;
>         unsigned int domain, bus, slot, func;
> -       struct pci_bus *pci_bus;
>         struct pci_dev *pci_dev;
>         char str[64];
>
> @@ -1032,13 +1031,8 @@ static int pcifront_detach_devices(struct pcifront_device *pdev)
>                         goto out;
>                 }
>
> -               pci_bus = pci_find_bus(domain, bus);
> -               if (!pci_bus) {
> -                       dev_dbg(&pdev->xdev->dev, "Cannot get bus %04x:%02x\n",
> -                               domain, bus);
> -                       continue;
> -               }
> -               pci_dev = pci_get_slot(pci_bus, PCI_DEVFN(slot, func));
> +               pci_dev = pci_get_domain_bus_and_slot(domain, bus,
> +                               PCI_DEVFN(slot, func));
>                 if (!pci_dev) {
>                         dev_dbg(&pdev->xdev->dev,
>                                 "Cannot get PCI device %04x:%02x:%02x.%d\n",
> --
> 1.7.9.5
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/