Re: [PATCH v6 10/30] PCI: Introduce pci_host_bridge_list to manage host bridges

[Yijing Wang]

On 2015/3/12 10:55, Bjorn Helgaas wrote:
> On Mon, Mar 09, 2015 at 10:34:07AM +0800, Yijing Wang wrote:
>> Introduce pci_host_bridge_list to manage pci host
>> bridges in system, so we could detect whether
>> the host in domain:bus is alreay registered.
>> Then we could remove bus alreay exist test in
>> __pci_create_root_bus().
> 
> It's a nice idea to move this test into the core.  While you're at it, why
> don't you check for any overlap with the bus ranges of existing host
> bridges?  For example, if we're trying to create a new host bridge to
> [bus 40-7f], it should conflict with existing bridges to [bus 00-7f]
> as well as to [bus 40-ff].  I think your current patch will detect the
> latter conflict but not the former.

Now pci host bridge may only know its start bus number, like acpi _BBN provided,
but does not limit the end bus number, Eg. two pci roots report _BBN 0x0 and 0x80,
so we have two bus number resource (0, 0xff) and (0x80, 0xff), if we check it strictly,
some pci scan would fail which currently scan success.

> 
>> Signed-off-by: Yijing Wang <wangyijing@xxxxxxxxxx>
>> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> ---
>>  drivers/pci/host-bridge.c |   24 +++++++++++++++++++++++-
>>  drivers/pci/probe.c       |    8 +-------
>>  include/linux/pci.h       |    1 +
>>  3 files changed, 25 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/host-bridge.c b/drivers/pci/host-bridge.c
>> index 3bd45e7..0bb08ef 100644
>> --- a/drivers/pci/host-bridge.c
>> +++ b/drivers/pci/host-bridge.c
>> @@ -8,6 +8,9 @@
>>  
>>  #include "pci.h"
>>  
>> +static LIST_HEAD(pci_host_bridge_list);
>> +static DEFINE_MUTEX(phb_mutex);
> 
> We don't use the "phb" abbreviation in the PCI core.

OK

> 
>> +
>>  static void pci_release_host_bridge_dev(struct device *dev)
>>  {
>>  	struct pci_host_bridge *bridge = to_pci_host_bridge(dev);
>> @@ -25,7 +28,7 @@ struct pci_host_bridge *pci_create_host_bridge(
>>  	int error;
>>  	int bus = PCI_BUSNUM(db);
>>  	int domain = PCI_DOMAIN(db);
>> -	struct pci_host_bridge *host;
>> +	struct pci_host_bridge *host, *temp;
>>  	struct resource_entry *window, *n;
>>  
>>  	host = kzalloc(sizeof(*host), GFP_KERNEL);
>> @@ -40,6 +43,18 @@ struct pci_host_bridge *pci_create_host_bridge(
>>  	 */
>>  	pci_host_assign_domain_nr(host);
>>  
>> +	mutex_lock(&phb_mutex);
>> +	list_for_each_entry(temp, &pci_host_bridge_list, list)
>> +		if (temp->domain == host->domain
>> +				&& temp->busnum == host->busnum) {
>> +			dev_dbg(&host->dev, "pci host bridge pci%04x:%02x exist\n",
>> +					host->domain, host->busnum);
> 
> &host->dev hasn't been initialized yet!  And the text of the original
> message was better.

Oh, my mistake, good catch.

> 
>> +			mutex_unlock(&phb_mutex);
>> +			kfree(host);
>> +			return NULL;
>> +		}
>> +	mutex_unlock(&phb_mutex);
> 
> This is racy.  Two CPUs adding a bridge to [bus 00-7f] at about the same
> time can both succeed.
> 

Hmm, I need to unlock after I add the new host bridge to the gloal host bridge list, thanks.

> And it needs curly braces around the list_for_each_entry() body.

OK

> 
>> +
>>  	host->dev.parent = parent;
>>  	INIT_LIST_HEAD(&host->windows);
>>  	host->dev.release = pci_release_host_bridge_dev;
>> @@ -55,11 +70,18 @@ struct pci_host_bridge *pci_create_host_bridge(
>>  	resource_list_for_each_entry_safe(window, n, resources)
>>  		list_move_tail(&window->node, &host->windows);
>>  
>> +	mutex_lock(&phb_mutex);
>> +	list_add_tail(&host->list, &pci_host_bridge_list);
>> +	mutex_unlock(&phb_mutex);
>>  	return host;
>>  }
>>  
>>  void pci_free_host_bridge(struct pci_host_bridge *host)
>>  {
>> +	mutex_lock(&phb_mutex);
>> +	list_del(&host->list);
>> +	mutex_unlock(&phb_mutex);
>> +
>>  	device_unregister(&host->dev);
>>  }
>>  
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index 27ec612..7238fa3 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1870,7 +1870,7 @@ static struct pci_bus *__pci_create_root_bus(
>>  		void *sysdata)
>>  {
>>  	int error;
>> -	struct pci_bus *b, *b2;
>> +	struct pci_bus *b;
>>  	struct resource_entry *window;
>>  	struct device *parent;
>>  	struct resource *res;
>> @@ -1887,12 +1887,6 @@ static struct pci_bus *__pci_create_root_bus(
>>  	b->ops = ops;
>>  	b->number = b->busn_res.start = bridge->busnum;
>>  	pci_bus_assign_domain_nr(b, parent);
>> -	b2 = pci_find_bus(pci_domain_nr(b), b->number);
>> -	if (b2) {
>> -		/* If we already got to this bus through a different bridge, ignore it */
>> -		dev_dbg(&b2->dev, "bus already known\n");
>> -		goto err_out;
>> -	}
>>  
>>  	bridge->bus = b;
>>  	b->bridge = get_device(&bridge->dev);
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 463eaa3..b621f5b 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -406,6 +406,7 @@ struct pci_host_bridge {
>>  	struct device dev;
>>  	struct pci_bus *bus;		/* root bus */
>>  	struct list_head windows;	/* resource_entry */
>> +	struct list_head list;
>>  	void (*release_fn)(struct pci_host_bridge *);
>>  	void *release_data;
>>  };
>> -- 
>> 1.7.1
>>
> 
> .
> 


-- 
Thanks!
Yijing

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