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Date: Tue, 07 Aug 2012 14:11:39 -0400
From: Don Dutile <ddutile@...hat.com>
To: Jiang Liu <liuj97@...il.com>
CC: Bjorn Helgaas <bhelgaas@...gle.com>,
Yinghai Lu <yinghai@...nel.org>,
Greg KH <gregkh@...uxfoundation.org>,
Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
Taku Izumi <izumi.taku@...fujitsu.com>,
"Rafael J . Wysocki" <rjw@...k.pl>,
Yijing Wang <wangyijing@...wei.com>,
Xinwei Hu <huxinwei@...wei.com>, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/22] introduce PCI bus lock to serialize PCI
hotplug operations
On 08/07/2012 12:10 PM, Jiang Liu wrote:
> From: Jiang Liu<liuj97@...il.com>
>
> This is the second take to resolve race conditions when hot-plugging PCI
> devices/host bridges. Instead of using a globla lock to serialize all hotplug
> operations as in previous version, now we introduce a state machine and bit
> lock mechanism for PCI buses to serialize hotplug operations. For discussions
> related to previous version, please refer to:
> http://comments.gmane.org/gmane.linux.kernel.pci/15007
>
> This patch-set is still in early stages, so sending it out just requesting
> for comments. Any comments are welcomed, especially about whether it's the
> right/suitable way to solve these race condition issues.
>
> patch 1-5:
> Preparing for coming PCI bus lock
> patch 6-7:
> Core of the new PCI bus lock mechanism.
> patch 8-13:
> Enhance PCI core to support PCI bus lock mechanism.
> patch 14-18:
> Enhance several PCI hotplug drivers to use PCI bus lock to serialize
> hotplug operations.
> patch 19-20:
> Enable PCI bus lock mechanism for x86 and IA64, still need to enable
> PCI bus lock for other archs.
> patch 21-22:
> Cleanups for unsed code.
>
> There are multiple methods to trigger PCI hotplug requests/operations
> concurrently, such as:
> 1. Sysfs interfaces exported by the PCI core subsystem
> /sys/devices/pcissss:bb/ssss:bb:dd.f/.../remove
> /sys/devices/pcissss:bb/ssss:bb:dd.f/.../rescan
> /sys/devices/pcissss:bb/ssss:bb:dd.f/.../pci_bus/ssss:bb/rescan
> /sys/bus/pci/rescan
> 2. Sysfs interfaces exported by the PCI hotplug subsystem
> /sys/bus/pci/slots/xx/power
> 3. PCI hotplug events triggered by PCI Hotplug Controllers
> 4. ACPI hotplug events for PCI host bridges
> 5. Driver binding/unbinding events
> binding/unbinding pci drivers with SR-IOV support
>
6. PCI reset
--> a PCIe device-level reset is done by KVM when it assigns a device
to a guest. a PCI config-save before reset, and PCI config-restore after reset
is done in this case.
--> VF devices are interesting, since they are reset, then bound to
pci-stub driver. when more than 1 VF is enabled in a PF,
and several device-assignments are done simultaneously, you
get a storm of reset (save/restore pci cfg space), and pci-stub binding
(pci cfg read for resource allocation/deallocation), and depending on
the hw design: an AER caused by the FLR reset -- not suppose to, but
hw has bugs too! ;-)
PCI locking is 'challenged' in the above scenario.
So, I ask: have you tried your patch set doing something like:
a) modprobe an SRIOV device with > 1 vf enabled
you may also have to do:
b) while assigning another SRIOV device's VF to another KVM guest
Unfortunately, the PCI cfg-space locking, esp. on x86 (ok, I'll say it:
damn, mutually exclusive, IO-port-based cfg registers), doesn't lend itself
to this multi-task, dynamic PCI scenario.
Much less complicated on linearly-mapped, PCI-mmconf-only accesses.
- Don
> With current implementation, the PCI core subsystem doesn't support
> concurrent hotplug operations yet. The existing pci_bus_sem lock only
> protects several lists in struct pci_bus, such as children list,
> devices list, but it doesn't protect the pci_bus or pci_dev structure
> themselves.
>
> Let's take pci_remove_bus_device() as an example, which are used by
> PCI hotplug drivers to hot-remove PCI devices. Currently all these
> are free running without any protection, so it can't support reentrance.
> pci_remove_bus_device()
> ->pci_stop_bus_device()
> ->pci_stop_bus_device()
> ->pci_stop_bus_devices()
> ->pci_stop_dev()
>
> Jiang Liu (22):
> PCI: use pci_get_domain_bus_and_slot() to avoid race conditions
> PCI: trivial cleanups for drivers/pci/remove.c
> PCI: change PCI device management code to better follow device model
> PCI: split PCI bus device registration into two stages
> PCI: introduce pci_bus_{get|put}() to manage PCI bus reference count
> PCI: use a global lock to serialize PCI root bridge hotplug
> operations
> PCI: introduce PCI bus lock to serialize PCI hotplug operations
> PCI: introduce hotplug safe search interfaces for PCI bus/device
> PCI: enhance PCI probe logic to support PCI bus lock mechanism
> PCI: enhance PCI bus specific logic to support PCI bus lock mechanism
> PCI: enhance PCI resource assignment logic to support PCI bus lock
> mechanism
> PCI: enhance PCI remove logic to support PCI bus lock mechanism
> PCI: make each PCI device hold a reference to its parent PCI bus
> PCI/sysfs: use PCI bus lock to avoid race conditions
> PCI/eeepc: use PCI bus lock to avoid race conditions
> PCI/asus-wmi: use PCI bus lock to avoid race conditions
> PCI/pciehp: use PCI bus lock to avoid race conditions
> PCI/acpiphp: use PCI bus lock to avoid race conditions
> PCI/x86: enable PCI bus lock mechanism for x86 platforms
> PCI/IA64: enable PCI bus lock mechanism for IA64 platforms
> PCI: cleanups for PCI bus lock implementation
> PCI: unexport pci_root_buses
>
> arch/ia64/pci/pci.c | 2 +
> arch/ia64/sn/kernel/io_common.c | 4 +-
> arch/ia64/sn/kernel/io_init.c | 1 +
> arch/ia64/sn/pci/tioca_provider.c | 4 +-
> arch/x86/pci/acpi.c | 6 +-
> arch/x86/pci/common.c | 12 +++
> drivers/acpi/pci_root.c | 8 +-
> drivers/edac/i7core_edac.c | 16 ++-
> drivers/gpu/drm/drm_fops.c | 6 +-
> drivers/gpu/vga/vgaarb.c | 15 +--
> drivers/pci/bus.c | 188 +++++++++++++++++++++++++++++-----
> drivers/pci/host-bridge.c | 19 ++++
> drivers/pci/hotplug/acpiphp_glue.c | 13 ++-
> drivers/pci/hotplug/cpcihp_generic.c | 8 +-
> drivers/pci/hotplug/pciehp_pci.c | 15 +++
> drivers/pci/hotplug/sgi_hotplug.c | 2 +
> drivers/pci/iov.c | 11 +-
> drivers/pci/pci-sysfs.c | 37 ++++---
> drivers/pci/probe.c | 83 +++++++++++----
> drivers/pci/remove.c | 176 +++++++++++++++++--------------
> drivers/pci/search.c | 53 ++++++++--
> drivers/pci/setup-bus.c | 65 +++++++++---
> drivers/pci/xen-pcifront.c | 10 +-
> drivers/platform/x86/asus-wmi.c | 23 ++++-
> drivers/platform/x86/eeepc-laptop.c | 20 ++--
> include/linux/pci.h | 56 +++++++++-
> 26 files changed, 629 insertions(+), 224 deletions(-)
>
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