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    SubjectRe: [RFC PATCH v1 01/22] PCI: use pci_get_domain_bus_and_slot() to avoid race conditions
    On Tue, Aug 7, 2012 at 10:10 AM, Jiang Liu <liuj97@gmail.com> 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@gmail.com>
    > ---
    > 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
    >


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