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Date: Tue, 11 Sep 2012 17:24:25 -0600
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Jiang Liu <liuj97@...il.com>
Cc: Don Dutile <ddutile@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
Greg KH <gregkh@...uxfoundation.org>,
Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
Jiang Liu <jiang.liu@...wei.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 07/22] PCI: introduce PCI bus lock to serialize PCI
hotplug operations
On Tue, Aug 7, 2012 at 10:10 AM, Jiang Liu <liuj97@...il.com> wrote:
> There are multiple ways to trigger concurrent PCI hotplug operations for
> a specific PCI bus, but we have no way to serialize those PCI hotplug
> operations yet and thus breaks the PCI hotplug logic. This patch introduces
> a bus lock mechanism and state machine for PCI buses to serialize PCI
> hotplug operations.
>
> The state machine for PCI buses is:
> __________________________ ______________
> | v | v
> INITIALIZED->REGISTERED->WORKING->STOPPING->STOPPED->REMOVED->DESTOYED
> |_________________________^
>
> The PCI buses is hierarchy, so need to obey the locking rules:
> 1) The PCI bus must be locked when changing any child devices of it.
> 2) The PCI bus must be locked when changing its state
> 3) The global PCI host bridge hotplug lock must be held when hotplugging
> PCI root buses
>
> The lock interfaces cordinated with the state machine will be used to
> avoid race conditions when hotplugging PCI devices/host bridges.
> A typical usage is (lock bus if it's in WORKING state, and then do hotplug):
> if (pci_bus_lock_states(bus, PCI_BUS_STATE_WORKING) > 0) {
> do_pci_hotplug();
> pci_bus_unlock(bus);
> }
>
> The PCI_BUS_LOCK config option is a temporary solution to avoid breaking
> bisect, it will be removed when all Archs have been converted to the new
> PCI bus lock mechanism.
I'm going to wait until I understand the global lock issues better
before I even look at these PCI bus lock patches.
> Signed-off-by: Jiang Liu <liuj97@...il.com>
> ---
> drivers/pci/Kconfig | 4 +++
> drivers/pci/bus.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 44 ++++++++++++++++++++++++++
> 3 files changed, 134 insertions(+)
>
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 848bfb8..a6df8b1 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -120,3 +120,7 @@ config PCI_IOAPIC
> config PCI_LABEL
> def_bool y if (DMI || ACPI)
> select NLS
> +
> +config PCI_BUS_LOCK
> + bool
> + default n
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 0e18270..aa25fcf 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -15,9 +15,12 @@
> #include <linux/proc_fs.h>
> #include <linux/init.h>
> #include <linux/slab.h>
> +#include <linux/sched.h>
>
> #include "pci.h"
>
> +static DECLARE_WAIT_QUEUE_HEAD(pci_bus_state_wait_queue);
> +
> void pci_add_resource_offset(struct list_head *resources, struct resource *res,
> resource_size_t offset)
> {
> @@ -340,6 +343,89 @@ void pci_bus_put(struct pci_bus *bus)
> }
> EXPORT_SYMBOL(pci_bus_put);
>
> +static bool pci_bus_wait_for_states(struct pci_bus *bus, int states)
> +{
> + int t = atomic_read(&bus->state);
> +
> + /* Bus state is bigger than any of the requested states. */
> + if ((t & PCI_BUS_STATE_MASK) > states)
> + return true;
> +
> + /* Bus is in one of the requested states and unlocked. */
> + if ((t & states) && !(t & PCI_BUS_STATE_LOCK))
> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * Wait for the bus to reach one of the requested states and then lock it.
> + * Return current bus state if succeed to lock the bus, and return -EINVAL
> + * if current bus state is already bigger than any of the requested states.
> + */
> +int pci_bus_lock_states(struct pci_bus *bus, int states)
> +{
> + int t;
> +
> + BUG_ON(states & ~PCI_BUS_STATE_MASK);
> + do {
> + do {
> + wait_event(pci_bus_state_wait_queue,
> + pci_bus_wait_for_states(bus, states));
> + t = atomic_read(&bus->state);
> + if ((t & PCI_BUS_STATE_MASK) > states)
> + return -EINVAL;
> + } while (!(t & states));
> +
> + t &= ~PCI_BUS_STATE_LOCK;
> + } while (atomic_cmpxchg(&bus->state, t , t | PCI_BUS_STATE_LOCK) != t);
> +
> + return t & PCI_BUS_STATE_MASK;
> +}
> +EXPORT_SYMBOL(pci_bus_lock_states);
> +
> +/* Unlock the bus and wake up waiters, must be called with the bus locked. */
> +void pci_bus_unlock(struct pci_bus *bus)
> +{
> + int t;
> +
> + BUG_ON(!pci_bus_is_locked(bus));
> + do {
> + t = atomic_read(&bus->state);
> + } while (atomic_cmpxchg(&bus->state,
> + t, t & ~PCI_BUS_STATE_LOCK) != t);
> +
> + if (waitqueue_active(&pci_bus_state_wait_queue))
> + wake_up_all(&pci_bus_state_wait_queue);
> +}
> +EXPORT_SYMBOL(pci_bus_unlock);
> +
> +/*
> + * Change the bus from old state to new state. It must be called with the bus
> + * locked, and the new state must be bigger than the old state.
> + */
> +void pci_bus_change_state(struct pci_bus *bus, int old, int new, bool unlock)
> +{
> + int t;
> +
> + BUG_ON(!pci_bus_is_locked(bus));
> + BUG_ON(new < old || pci_bus_get_state(bus) != old ||
> + (new & ~PCI_BUS_STATE_MASK));
> +
> + old |= PCI_BUS_STATE_LOCK;
> + if (!unlock)
> + new |= PCI_BUS_STATE_LOCK;
> +
> + do {
> + t = atomic_read(&bus->state);
> + t &= ~(PCI_BUS_STATE_MASK | PCI_BUS_STATE_LOCK);
> + } while (atomic_cmpxchg(&bus->state, t | old, t | new) != (t | old));
> +
> + if (waitqueue_active(&pci_bus_state_wait_queue))
> + wake_up_all(&pci_bus_state_wait_queue);
> +}
> +EXPORT_SYMBOL(pci_bus_change_state);
> +
> EXPORT_SYMBOL(pci_bus_alloc_resource);
> EXPORT_SYMBOL_GPL(pci_bus_add_device);
> EXPORT_SYMBOL(pci_bus_add_devices);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e02f130..e2ef517 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -443,8 +443,52 @@ struct pci_bus {
> struct bin_attribute *legacy_io; /* legacy I/O for this bus */
> struct bin_attribute *legacy_mem; /* legacy mem */
> unsigned int is_added:1;
> + atomic_t state;
> };
>
> +/*
> + * State machine for PCI buses.
> + * __________________________ ______________
> + * | v | v
> + * INITIALIZED->REGISTERED->WORKING->STOPPING->STOPPED->REMOVED->DESTOYED
> + * |_________________________^
> + */
> +#define PCI_BUS_STATE_UNKNOWN 0x0 /* invalid state */
> +#define PCI_BUS_STATE_INITIALIZED 0x1 /* device_initialize called */
> +#define PCI_BUS_STATE_REGISTERED 0x2 /* device_add called */
> +#define PCI_BUS_STATE_WORKING 0x4 /* working state */
> +#define PCI_BUS_STATE_STOPPING 0x8 /* stopping devices */
> +#define PCI_BUS_STATE_STOPPED 0x10 /* device_del called */
> +#define PCI_BUS_STATE_REMOVED 0x20 /* bus deleted */
> +#define PCI_BUS_STATE_DESTROYED 0x40 /* invalid state */
> +#define PCI_BUS_STATE_MASK 0x7F
> +
> +#ifdef CONFIG_PCI_BUS_LOCK
> +#define PCI_BUS_STATE_LOCK 0x10000 /* for pci core only */
> +
> +static inline bool pci_bus_is_locked(struct pci_bus *bus)
> +{
> + return !!(atomic_read(&bus->state) & PCI_BUS_STATE_LOCK);
> +}
> +#else /* CONFIG_PCI_BUS_LOCK */
> +#define PCI_BUS_STATE_LOCK 0x0000 /* for pci core only */
> +
> +static inline bool pci_bus_is_locked(struct pci_bus *bus)
> +{
> + return true;
> +}
> +#endif /* CONFIG_PCI_BUS_LOCK */
> +
> +static inline int pci_bus_get_state(struct pci_bus *bus)
> +{
> + return atomic_read(&bus->state) & PCI_BUS_STATE_MASK;
> +}
> +
> +extern int pci_bus_lock_states(struct pci_bus *bus, int states);
> +extern void pci_bus_unlock(struct pci_bus *bus);
> +extern void pci_bus_change_state(struct pci_bus *bus, int new, int old,
> + bool unlock);
> +
> #define pci_bus_b(n) list_entry(n, struct pci_bus, node)
> #define to_pci_bus(n) container_of(n, struct pci_bus, dev)
>
> --
> 1.7.9.5
>
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