[PATCH v3] PCI: Data corruption happening due to race condition
Bjorn Helgaas
helgaas at kernel.org
Thu Jul 19 09:29:07 AEST 2018
[+cc Paul, Michael, linuxppc-dev]
On Tue, Jul 03, 2018 at 02:35:41PM +0530, Hari Vyas wrote:
> When a pci device is detected, a variable is_added is set to
> 1 in pci device structure and proc, sys entries are created.
>
> When a pci device is removed, first is_added is checked for one
> and then device is detached with clearing of proc and sys
> entries and at end, is_added is set to 0.
>
> is_added and is_busmaster are bit fields in pci_dev structure
> sharing same memory location.
>
> A strange issue was observed with multiple times removal and
> rescan of a pcie nvme device using sysfs commands where is_added
> flag was observed as zero instead of one while removing device
> and proc,sys entries are not cleared. This causes issue in
> later device addition with warning message "proc_dir_entry"
> already registered.
>
> Debugging revealed a race condition between pcie core driver
> enabling is_added bit(pci_bus_add_device()) and nvme driver
> reset work-queue enabling is_busmaster bit (by pci_set_master()).
> As both fields are not handled in atomic manner and that clears
> is_added bit.
>
> Fix moves device addition is_added bit to separate private flag
> variable and use different atomic functions to set and retrieve
> device addition state. As is_added shares different memory
> location so race condition is avoided.
Really nice bit of debugging!
> Signed-off-by: Hari Vyas <hari.vyas at broadcom.com>
> ---
> arch/powerpc/kernel/pci-common.c | 4 +++-
> arch/powerpc/platforms/powernv/pci-ioda.c | 3 ++-
> arch/powerpc/platforms/pseries/setup.c | 3 ++-
> drivers/pci/bus.c | 6 +++---
> drivers/pci/hotplug/acpiphp_glue.c | 2 +-
> drivers/pci/pci.h | 11 +++++++++++
> drivers/pci/probe.c | 4 ++--
> drivers/pci/remove.c | 5 +++--
> include/linux/pci.h | 1 -
> 9 files changed, 27 insertions(+), 12 deletions(-)
>
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index fe9733f..471aac3 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -42,6 +42,8 @@
> #include <asm/ppc-pci.h>
> #include <asm/eeh.h>
>
> +#include "../../../drivers/pci/pci.h"
I see why you need it, but this include path is really ugly. Outside
of bootloaders and tools, there are very few instances of includes
like this that reference a different top-level directory, and I'm not
very keen about adding more.
Obviously powerpc is the only arch that needs dev->is_added. It seems
to be because "We can only call pcibios_setup_device() after bus setup
is complete, since some of the platform specific DMA setup code
depends on it."
I don't know powerpc, but it does raise the question in my mind of
whether powerpc could be changed to do the DMA setup more like other
arches do to remove this ordering dependency and the need to use
dev->is_added.
That sounds like a lot of work, but it would have the benefit of
unifying some code that is probably needlessly arch-specific.
> /* hose_spinlock protects accesses to the the phb_bitmap. */
> static DEFINE_SPINLOCK(hose_spinlock);
> LIST_HEAD(hose_list);
> @@ -1014,7 +1016,7 @@ void pcibios_setup_bus_devices(struct pci_bus *bus)
> /* Cardbus can call us to add new devices to a bus, so ignore
> * those who are already fully discovered
> */
> - if (dev->is_added)
> + if (pci_dev_is_added(dev))
> continue;
>
> pcibios_setup_device(dev);
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 5bd0eb6..70b2e1e 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -46,6 +46,7 @@
>
> #include "powernv.h"
> #include "pci.h"
> +#include "../../../../drivers/pci/pci.h"
>
> #define PNV_IODA1_M64_NUM 16 /* Number of M64 BARs */
> #define PNV_IODA1_M64_SEGS 8 /* Segments per M64 BAR */
> @@ -3138,7 +3139,7 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
> struct pci_dn *pdn;
> int mul, total_vfs;
>
> - if (!pdev->is_physfn || pdev->is_added)
> + if (!pdev->is_physfn || pci_dev_is_added(pdev))
> return;
>
> pdn = pci_get_pdn(pdev);
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index 139f0af..8a4868a 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -71,6 +71,7 @@
> #include <asm/security_features.h>
>
> #include "pseries.h"
> +#include "../../../../drivers/pci/pci.h"
>
> int CMO_PrPSP = -1;
> int CMO_SecPSP = -1;
> @@ -664,7 +665,7 @@ static void pseries_pci_fixup_iov_resources(struct pci_dev *pdev)
> const int *indexes;
> struct device_node *dn = pci_device_to_OF_node(pdev);
>
> - if (!pdev->is_physfn || pdev->is_added)
> + if (!pdev->is_physfn || pci_dev_is_added(pdev))
> return;
> /*Firmware must support open sriov otherwise dont configure*/
> indexes = of_get_property(dn, "ibm,open-sriov-vf-bar-info", NULL);
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 35b7fc8..5cb40b2 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -330,7 +330,7 @@ void pci_bus_add_device(struct pci_dev *dev)
> return;
> }
>
> - dev->is_added = 1;
> + pci_dev_assign_added(dev, true);
> }
> EXPORT_SYMBOL_GPL(pci_bus_add_device);
>
> @@ -347,14 +347,14 @@ void pci_bus_add_devices(const struct pci_bus *bus)
>
> list_for_each_entry(dev, &bus->devices, bus_list) {
> /* Skip already-added devices */
> - if (dev->is_added)
> + if (pci_dev_is_added(dev))
> continue;
> pci_bus_add_device(dev);
> }
>
> list_for_each_entry(dev, &bus->devices, bus_list) {
> /* Skip if device attach failed */
> - if (!dev->is_added)
> + if (!pci_dev_is_added(dev))
> continue;
> child = dev->subordinate;
> if (child)
> diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> index 3a17b29..ef0b1b6 100644
> --- a/drivers/pci/hotplug/acpiphp_glue.c
> +++ b/drivers/pci/hotplug/acpiphp_glue.c
> @@ -509,7 +509,7 @@ static void enable_slot(struct acpiphp_slot *slot)
>
> list_for_each_entry(dev, &bus->devices, bus_list) {
> /* Assume that newly added devices are powered on already. */
> - if (!dev->is_added)
> + if (!pci_dev_is_added(dev))
> dev->current_state = PCI_D0;
> }
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 882f1f9..0881725 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -288,6 +288,7 @@ struct pci_sriov {
>
> /* pci_dev priv_flags */
> #define PCI_DEV_DISCONNECTED 0
> +#define PCI_DEV_ADDED 1
>
> static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
> {
> @@ -300,6 +301,16 @@ static inline bool pci_dev_is_disconnected(const struct pci_dev *dev)
> return test_bit(PCI_DEV_DISCONNECTED, &dev->priv_flags);
> }
>
> +static inline void pci_dev_assign_added(struct pci_dev *dev, bool added)
> +{
> + assign_bit(PCI_DEV_ADDED, &dev->priv_flags, added);
> +}
> +
> +static inline bool pci_dev_is_added(const struct pci_dev *dev)
> +{
> + return test_bit(PCI_DEV_ADDED, &dev->priv_flags);
> +}
> +
> #ifdef CONFIG_PCI_ATS
> void pci_restore_ats_state(struct pci_dev *dev);
> #else
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ac876e3..611adcd 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2433,13 +2433,13 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
> dev = pci_scan_single_device(bus, devfn);
> if (!dev)
> return 0;
> - if (!dev->is_added)
> + if (!pci_dev_is_added(dev))
> nr++;
>
> for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) {
> dev = pci_scan_single_device(bus, devfn + fn);
> if (dev) {
> - if (!dev->is_added)
> + if (!pci_dev_is_added(dev))
> nr++;
> dev->multifunction = 1;
> }
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 6f072ea..5e3d0dc 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -19,11 +19,12 @@ static void pci_stop_dev(struct pci_dev *dev)
> {
> pci_pme_active(dev, false);
>
> - if (dev->is_added) {
> + if (pci_dev_is_added(dev)) {
> device_release_driver(&dev->dev);
> pci_proc_detach_device(dev);
> pci_remove_sysfs_dev_files(dev);
> - dev->is_added = 0;
> +
> + pci_dev_assign_added(dev, false);
> }
>
> if (dev->bus->self)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 340029b..506125b 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -368,7 +368,6 @@ struct pci_dev {
> unsigned int transparent:1; /* Subtractive decode bridge */
> unsigned int multifunction:1; /* Multi-function device */
>
> - unsigned int is_added:1;
> unsigned int is_busmaster:1; /* Is busmaster */
> unsigned int no_msi:1; /* May not use MSI */
> unsigned int no_64bit_msi:1; /* May only use 32-bit MSIs */
> --
> 1.9.1
>
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