>>>>> This list_del() updates the bus->slots list.
>>>>
>>>> It's safe here, because we have locked the pci_slot_mutex in pci_destroy_slot(), which is the only caller of pci_slot_release().
>>>
>>> That doesn't protect anybody else who might be traversing the
>>> bus->slots list while we're deleting this entry.
>>
>> Hi Bjorn, sorry, I don't understand your point, before this patch, we use pci_bus_sem to protect the whole pci_slot_release(),
>> in which, we would traverse the bus->devices list and update the bus->slots list. And now what we did is introduce a new pci_slot_mutex
>> to protect the bus->slots here, and use down_read(pci_bus_sem) instead of down_write(pci_bus_sem).
>
> pci_setup_device() does this:
>
> list_for_each_entry(slot, &dev->bus->slots, list)
> if (PCI_SLOT(dev->devfn) == slot->number)
> dev->slot = slot;
>
> What keeps that code from running at the same time pci_slot_release()
> is removing something from the bus->slots list?
>
> It looks to me like the loop in pci_setup_device() is unsafe to begin
> with. But the obvious thing to do would be to add
> down_read(&pci_bus_sem) there, and then you'd need a down_write() in
> pci_slot_release(), so you're back where we started.
I got it, I missed the bus->slots list traverse in pci scan code,
What about moving the bus->slots loop code from pci_setup_device() to drivers/pci/slot.c, and add a pci_slot_mutex to protect it ?
I think we should avoid to use pci_bus_sem to protect bus->slots list.
Something like this:
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index cefd636..6f00273 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1149,10 +1149,7 @@ int pci_setup_device(struct pci_dev *dev)
dev->error_state = pci_channel_io_normal;
set_pcie_port_type(dev);
- list_for_each_entry(slot, &dev->bus->slots, list)
- if (PCI_SLOT(dev->devfn) == slot->number)
- dev->slot = slot;
-
+ pci_dev_assign_slot(dev);
/* Assume 32-bit PCI; let 64-bit PCI cards (which are far rarer)
set this higher, assuming the system even supports it. */
dev->dma_mask = 0xffffffff;
diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index a9079d9..cf259e7 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -99,6 +99,15 @@ static ssize_t cur_speed_read_file(struct pci_slot *slot, char *buf)
return bus_speed_read(slot->bus->cur_bus_speed, buf);
}
+void pci_dev_assign_slot(struct pci_dev *dev)
+{
+ mutex_lock(&pci_slot_mutex);
+ list_for_each_entry(slot, &dev->bus->slots, list)
+ if (PCI_SLOT(dev->devfn) == slot->number)
+ dev->slot = slot;
+ mutex_unlock(&pci_slot_mutex);
+}
+
static void pci_slot_release(struct kobject *kobj)
{
struct pci_dev *dev;
>
>>>>>> @@ -195,7 +198,7 @@ static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)
>>>>>> {
>>>>>> struct pci_slot *slot;
>>>>>> /*
>>>>>> - * We already hold pci_bus_sem so don't worry
>>>>>> + * We already hold pci_slot_mutex so don't worry
>>>>>> */
>>>>>> list_for_each_entry(slot, &parent->slots, list)
>>>>>> if (slot->number == slot_nr) {
>>>>>> @@ -253,7 +256,7 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
>>>>>> int err = 0;
>>>>>> char *slot_name = NULL;
>>>>>>
>>>>>> - down_write(&pci_bus_sem);
>>>>>> + mutex_lock(&pci_slot_mutex);
>>>>>>
>>>>>> if (slot_nr == -1)
>>>>>> goto placeholder;
>>>>>> @@ -301,16 +304,18 @@ placeholder:
>>>>>> INIT_LIST_HEAD(&slot->list);
>>>>>> list_add(&slot->list, &parent->slots);
>>>>>>
>>>>>> + down_read(&pci_bus_sem);
>>>>>> list_for_each_entry(dev, &parent->devices, bus_list)
>>>>>> if (PCI_SLOT(dev->devfn) == slot_nr)
>>>>>> dev->slot = slot;
>>>>>> + up_read(&pci_bus_sem);
>>>>>>
>>>>>> dev_dbg(&parent->dev, "dev %02x, created physical slot %s\n",
>>>>>> slot_nr, pci_slot_name(slot));
>>>>>>
>>>>>> out:
>>>>>> kfree(slot_name);
>>>>>> - up_write(&pci_bus_sem);
>>>>>> + mutex_unlock(&pci_slot_mutex);
>>>>>> return slot;
>>>>>> err:
>>>>>> kfree(slot);
>>>>>> @@ -332,9 +337,9 @@ void pci_destroy_slot(struct pci_slot *slot)
>>>>>> dev_dbg(&slot->bus->dev, "dev %02x, dec refcount to %d\n",
>>>>>> slot->number, atomic_read(&slot->kobj.kref.refcount) - 1);
>>>>>>
>>>>>> - down_write(&pci_bus_sem);
>>>>>> + mutex_lock(&pci_slot_mutex);
>>>>>> kobject_put(&slot->kobj);
>>>>>> - up_write(&pci_bus_sem);
>>>>>> + mutex_unlock(&pci_slot_mutex);
>>>>>> }
>>>>>> EXPORT_SYMBOL_GPL(pci_destroy_slot);
>>>>>
>>>>> .
>>>>>
>>>>
>>>>
>>>> --
>>>> Thanks!
>>>> Yijing
>>>>
>>>
>>> .
>>>
>>
>>
>> --
>> Thanks!
>> Yijing
>>
>
> .
>
--
Thanks!
Yijing
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