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Message-ID: <CAErSpo7u=_H=c0UBte7fuQAML4KWErDhsmZ+E8LTzW7OPWzpXA@mail.gmail.com>
Date: Mon, 12 Mar 2012 21:49:20 -0600
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Jiang Liu <liuj97@...il.com>
Cc: Yinghai Lu <yinghai@...nel.org>,
Jesse Barnes <jbarnes@...tuousgeek.org>,
Jiang Liu <jiang.liu@...wei.com>,
Ashok Raj <ashok.raj@...el.com>,
Suresh Siddha <suresh.b.siddha@...el.com>,
Youquan Song <youquan.song@...el.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
chenkeping@...wei.com
Subject: Re: [RFC PATCH 4/5] PCI: Introduce hotplug-safe pci bus searching interfaces
On Sun, Mar 11, 2012 at 11:48 AM, Jiang Liu <liuj97@...il.com> wrote:
> By design, pci_find_bus() and pci_find_next_bus() should be used at boot
> time only. But currently these two interfaces have been used at runtime
> by other components. With the introduction of pci root bus hotplug,
> the situation becomes more serious. So introduce several hotplug-safe pci
> bus searching interfaces to be used at runtime. The new interfaces use
> rculist instead of the pci_bus_sem to protect themselves from dynamic changes.
> The proposed interfaces are straight-forward replacement of the old ones:
> pci_bus_get()/put(), pci_get_bus(), pci_get_next_bus() and pci_bus_present().
> And the old interface may be deprecated or marked as __init in future.
This looks like a lot of work to fix something that shouldn't need to
be fixed. I don't think we should be doing any of this blind probing
at hotplug-time. If we do blind probing at all, it should only be
done at boot-time.
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> ---
> drivers/pci/bus.c | 20 ++++++-
> drivers/pci/probe.c | 5 +-
> drivers/pci/remove.c | 5 +-
> drivers/pci/search.c | 165 ++++++++++++++++++++++++++++++++++++++++++--------
> include/linux/pci.h | 8 +++
> 5 files changed, 173 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 1eb7944..0543d47 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -15,6 +15,7 @@
> #include <linux/proc_fs.h>
> #include <linux/init.h>
> #include <linux/slab.h>
> +#include <linux/rculist.h>
>
> #include "pci.h"
>
> @@ -238,7 +239,7 @@ void pci_bus_add_devices(const struct pci_bus *bus)
> continue;
> if (list_empty(&child->node)) {
> down_write(&pci_bus_sem);
> - list_add_tail(&child->node, &dev->bus->children);
> + list_add_tail_rcu(&child->node, &dev->bus->children);
> up_write(&pci_bus_sem);
> }
> pci_bus_add_devices(child);
> @@ -277,7 +278,7 @@ void pci_bus_add_single_device(struct pci_dev *dev)
> if (child) {
> if (list_empty(&child->node)) {
> down_write(&pci_bus_sem);
> - list_add_tail(&child->node, &dev->bus->children);
> + list_add_tail_rcu(&child->node, &dev->bus->children);
> up_write(&pci_bus_sem);
> }
> pci_bus_add_devices(child);
> @@ -364,6 +365,21 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> }
> EXPORT_SYMBOL_GPL(pci_walk_bus);
>
> +struct pci_bus *pci_bus_get(struct pci_bus *bus)
> +{
> + if (bus)
> + get_device(&bus->dev);
> + return bus;
> +}
> +EXPORT_SYMBOL(pci_bus_get);
> +
> +void pci_bus_put(struct pci_bus *bus)
> +{
> + if (bus)
> + put_device(&bus->dev);
> +}
> +EXPORT_SYMBOL(pci_bus_put);
> +
> EXPORT_SYMBOL(pci_bus_alloc_resource);
> EXPORT_SYMBOL_GPL(pci_bus_add_device);
> EXPORT_SYMBOL(pci_bus_add_devices);
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 0ca213c..273c387 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -10,6 +10,7 @@
> #include <linux/module.h>
> #include <linux/cpumask.h>
> #include <linux/pci-aspm.h>
> +#include <linux/rculist.h>
> #include "pci.h"
>
> #define CARDBUS_LATENCY_TIMER 176 /* secondary latency timer */
> @@ -633,7 +634,7 @@ struct pci_bus *__ref pci_add_new_bus(struct pci_bus *parent, struct pci_dev *de
> child = pci_alloc_child_bus(parent, dev, busnr);
> if (child) {
> down_write(&pci_bus_sem);
> - list_add_tail(&child->node, &parent->children);
> + list_add_tail_rcu(&child->node, &parent->children);
> up_write(&pci_bus_sem);
> }
> return child;
> @@ -1889,7 +1890,7 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
> }
>
> down_write(&pci_bus_sem);
> - list_add_tail(&b->node, &pci_root_buses);
> + list_add_tail_rcu(&b->node, &pci_root_buses);
> up_write(&pci_bus_sem);
>
> return b;
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 25f368e..120bee9 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -1,6 +1,7 @@
> #include <linux/pci.h>
> #include <linux/module.h>
> #include <linux/pci-aspm.h>
> +#include <linux/rculist.h>
> #include "pci.h"
>
> static void pci_free_resources(struct pci_dev *dev)
> @@ -67,9 +68,11 @@ void pci_remove_bus(struct pci_bus *pci_bus)
> pci_proc_detach_bus(pci_bus);
>
> down_write(&pci_bus_sem);
> - list_del(&pci_bus->node);
> + list_del_rcu(&pci_bus->node);
> pci_bus_release_busn_res(pci_bus);
> up_write(&pci_bus_sem);
> + synchronize_rcu();
> +
> if (pci_bus->is_added || pci_is_root_bus(pci_bus)) {
> pci_remove_legacy_files(pci_bus);
> device_unregister(&pci_bus->dev);
> diff --git a/drivers/pci/search.c b/drivers/pci/search.c
> index b572730..de31957 100644
> --- a/drivers/pci/search.c
> +++ b/drivers/pci/search.c
> @@ -12,6 +12,7 @@
> #include <linux/slab.h>
> #include <linux/module.h>
> #include <linux/interrupt.h>
> +#include <linux/rculist.h>
> #include "pci.h"
>
> DECLARE_RWSEM(pci_bus_sem);
> @@ -52,20 +53,63 @@ pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
>
> static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
> {
> - struct pci_bus* child;
> - struct list_head *tmp;
> + struct pci_bus *child;
> + struct pci_bus *tmp_bus;
>
> if(bus->number == busnr)
> return bus;
>
> - list_for_each(tmp, &bus->children) {
> - child = pci_do_find_bus(pci_bus_b(tmp), busnr);
> - if(child)
> - return child;
> + list_for_each_entry_rcu(child, &bus->children, node) {
> + tmp_bus = pci_do_find_bus(child, busnr);
> + if(tmp_bus)
> + return tmp_bus;
> }
> return NULL;
> }
>
> +static struct pci_bus *__pci_find_bus(int domain, int busnr)
> +{
> + struct pci_bus *bus;
> + struct pci_bus *tmp_bus;
> +
> + list_for_each_entry_rcu(bus, &pci_root_buses, node) {
> + if (pci_domain_nr(bus) != domain)
> + continue;
> + tmp_bus = pci_do_find_bus(bus, busnr);
> + if (tmp_bus)
> + return tmp_bus;
> + }
> +
> + return NULL;
> +}
> +
> +static struct pci_bus *__pci_find_next_bus(const struct pci_bus *from)
> +{
> + struct list_head *n;
> + struct pci_bus *b = NULL;
> +
> + /* First search, start from the pci root bus list */
> + if (from == NULL) {
> + n = rcu_dereference(list_next_rcu(&pci_root_buses));
> + if (n != &pci_root_buses)
> + b = pci_bus_b(n);
> + /* Continue on the pci root bus list */
> + } else if (pci_is_root_bus((struct pci_bus *)from)) {
> + n = rcu_dereference(list_next_rcu(&from->node));
> + if (n != &pci_root_buses)
> + b = pci_bus_b(n);
> + /* Continue on other non pci root bus list */
> + } else {
> + struct pci_bus *parent = from->self->bus;
> +
> + n = rcu_dereference(list_next_rcu(&from->node));
> + if (n != &parent->children)
> + b = pci_bus_b(n);
> + }
> +
> + return b;
> +}
> +
> /**
> * pci_find_bus - locate PCI bus from a given domain and bus number
> * @domain: number of PCI domain to search
> @@ -74,20 +118,19 @@ static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
> * Given a PCI bus number and domain number, the desired PCI bus is located
> * in the global list of PCI buses. If the bus is found, a pointer to its
> * data structure is returned. If no bus is found, %NULL is returned.
> + *
> + * TODO: By design, this function should only be called at boot time.
> + * So either mark it as __init or deprecate it.
> */
> struct pci_bus * pci_find_bus(int domain, int busnr)
> {
> - struct pci_bus *bus = NULL;
> - struct pci_bus *tmp_bus;
> + struct pci_bus *bus;
>
> - while ((bus = pci_find_next_bus(bus)) != NULL) {
> - if (pci_domain_nr(bus) != domain)
> - continue;
> - tmp_bus = pci_do_find_bus(bus, busnr);
> - if (tmp_bus)
> - return tmp_bus;
> - }
> - return NULL;
> + rcu_read_lock();
> + bus = __pci_find_bus(domain, busnr);
> + rcu_read_unlock();
> +
> + return bus;
> }
>
> /**
> @@ -98,21 +141,93 @@ struct pci_bus * pci_find_bus(int domain, int busnr)
> * initiated by passing %NULL as the @from argument. Otherwise if
> * @from is not %NULL, searches continue from next device on the
> * global list.
> + *
> + * TODO: By design, this function should only be called at boot time.
> + * So either mark it as __init or deprecate it.
> */
> struct pci_bus *
> pci_find_next_bus(const struct pci_bus *from)
> {
> - struct list_head *n;
> - struct pci_bus *b = NULL;
> + struct pci_bus *bus;
>
> - WARN_ON(in_interrupt());
> - down_read(&pci_bus_sem);
> - n = from ? from->node.next : pci_root_buses.next;
> - if (n != &pci_root_buses)
> - b = pci_bus_b(n);
> - up_read(&pci_bus_sem);
> - return b;
> + rcu_read_lock();
> + bus = __pci_find_next_bus(from);
> + rcu_read_unlock();
> +
> + return bus;
> +}
> +
> +/**
> + * pci_get_bus - locate PCI bus from a given domain and bus number
> + * @domain: number of PCI domain to search
> + * @busnr: number of desired PCI bus
> + *
> + * Given a PCI bus number and domain number, the desired PCI bus is located
> + * in the global list of PCI buses. If the bus is found, a pointer to its
> + * data structure is returned, and the reference count to the bus is increased.
> + * Otherwise, %NULL is returned.
> + */
> +struct pci_bus *
> +pci_get_bus(int domain, int busnr)
> +{
> + struct pci_bus *bus;
> +
> + rcu_read_lock();
> + bus = pci_bus_get(__pci_find_bus(domain, busnr));
> + rcu_read_unlock();
> +
> + return bus;
> +}
> +EXPORT_SYMBOL(pci_get_bus);
> +
> +/**
> + * pci_get_next_bus - begin or continue searching for a PCI bus
> + * @from: Previous PCI bus found, or %NULL for new search.
> + *
> + * Iterates through the list of known PCI busses. A new search is
> + * initiated by passing %NULL as the @from argument. Otherwise if
> + * @from is not %NULL, searches continue from next device on the
> + * global list. If a bus is found, a pointer to its data structure
> + * is returned, and the reference count to the bus is increased.
> + * Otherwise, %NULL is returned.
> + * The reference count for @from is always decremented if it is not %NULL.
> + */
> +struct pci_bus *
> +pci_get_next_bus(struct pci_bus *from)
> +{
> + struct pci_bus *bus;
> +
> + rcu_read_lock();
> + bus = pci_bus_get(__pci_find_next_bus(from));
> + rcu_read_unlock();
> +
> + return bus;
> +}
> +EXPORT_SYMBOL(pci_get_next_bus);
> +
> +/**
> + * pci_bus_present - Returns true if a bus with the (@domain, @busnr)
> + * is present, false if not.
> + * @domain: number of PCI domain to search
> + * @busnr: number of desired PCI bus
> + *
> + * Obvious fact: You do not have a reference to any bus that might be found
> + * by this function, so if that bus is removed from the system right after
> + * this function is finished, the value will be stale. Use this function to
> + * find buses that are usually built into a system, or for a general hint as
> + * to if another device happens to be present at this specific moment in time.
> + */
> +bool pci_bus_present(int domain, int busnr)
> +{
> + struct pci_bus *bus;
> +
> + rcu_read_lock();
> + bus = __pci_find_bus(domain, busnr);
> + rcu_read_unlock();
> +
> + return !!bus;
> }
> +EXPORT_SYMBOL(pci_bus_present);
>
> /**
> * pci_get_slot - locate PCI device for a given PCI slot
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index ec8c4cf..222bc88 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -731,6 +731,11 @@ int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
> int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
> struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
>
> +struct pci_bus *pci_bus_get(struct pci_bus *bus);
> +void pci_bus_put(struct pci_bus *bus);
> +struct pci_bus *pci_get_bus(int domain, int busnr);
> +struct pci_bus *pci_get_next_bus(struct pci_bus *from);
> +bool pci_bus_present(int domain, int busnr);
> struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
> struct pci_dev *from);
> struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
> @@ -1321,6 +1326,9 @@ static inline void pci_unblock_cfg_access(struct pci_dev *dev)
> static inline struct pci_bus *pci_find_next_bus(const struct pci_bus *from)
> { return NULL; }
>
> +static inline struct pci_bus *pci_get_next_bus(const struct pci_bus *from)
> +{ return NULL; }
> +
> static inline struct pci_dev *pci_get_slot(struct pci_bus *bus,
> unsigned int devfn)
> { return NULL; }
> --
> 1.7.5.4
>
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