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Date: Tue, 10 Jun 2008 11:34:08 -0600
From: Alex Chiang <achiang@...com>
To: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
Cc: jbarnes@...tuousgeek.org,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Matthew Wilcox <matthew@....cx>,
Andrew Morton <akpm@...ux-foundation.org>,
kristen.c.accardi@...el.com, greg@...ah.com, lenb@...nel.org,
pbadari@...ibm.com, linux-pci@...r.kernel.org,
pcihpd-discuss@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4, v14] PCI, ACPI: Physical PCI slot objects
Hi Kenji-san,
* Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>:
> Alex Chiang wrote:
> > * Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>:
> >> I tried your patches and I have a comment (question) about the behavior.
> >>
> >> To emulate the (broken?) platform that assigns the same name to multiple
> >> slots, I made a debug patch for pciehp driver to assign same name ('1000')
> >> to all slots (my environment has two PCIe slots). With this patch, I
> >> noticed that the behavior or pci_hp_register() (or pci_create_slot())
> >> varies depending on whether pci_slot driver is loaded or not. See below.
> >>
> >> (a) With pci_slot driver loaded
> >> I got the following error message when I loaded pciehp driver.
> >>
> >> pciehp: pci_hp_register failed with error -17
> >> pciehp: Failed to register slot because of name collision. Try
> >> 'pciehp_slot_with_bus' module option.
> >> pciehp: pciehp: slot initialization failed
> >> (b) Without pci_slot driver loaded
> >> I got the kernel stack dump and error messages when I loaded pciehp
> >> driver.
> >>
> >> kobject_add_internal failed for 1000 with -EEXIST, don't try to
> >> register things with the same name in the same directory.
> >>
> >> Call Trace:
> >> [<a000000100015180>] show_stack+0x40/0xa0
> >> sp=e0000040a086fb80 bsp=e0000040a0861158
> >> [<a000000100015210>] dump_stack+0x30/0x60
> >> sp=e0000040a086fd50 bsp=e0000040a0861140
> >> [<a0000001003b3910>] kobject_add_internal+0x330/0x400
> >> sp=e0000040a086fd50 bsp=e0000040a0861100
> >> [<a0000001003b3bd0>] kobject_add_varg+0x90/0xc0
> >> sp=e0000040a086fd50 bsp=e0000040a08610c8
> >> [<a0000001003b3c90>] kobject_init_and_add+0x90/0xc0
> >> sp=e0000040a086fd50 bsp=e0000040a0861068
> >> [<a0000001003d69b0>] pci_create_slot+0x150/0x260
> >> sp=e0000040a086fd80 bsp=e0000040a0861030
> >> [<a000000200b71870>] pci_hp_register+0x130/0x880 [pci_hotplug]
> >> sp=e0000040a086fd80 bsp=e0000040a0860ff0
> >> [<a000000200ec1a60>] pciehp_probe+0x720/0xca0 [pciehp]
> >>
> >> (snip...)
> >>
> >> Unable to register kobject 1000
> >> pciehp: pci_hp_register failed with error -17
> >> pciehp: Failed to register slot because of name collision. Try
> >> 'pciehp_slot_with_bus' module option.
> >> pciehp: pciehp: slot initialization failed
> >>
> >> Could you tell me why that difference happen? And my expectation is
> >> the result should be (a) above regardless of whether pci_slot driver
> >> is loaded or not.
> >
> > The difference was because in (a), pci_slot created the slots and
> > when pciehp tried to register them, the pci slot infrastructure
> > simply refcounted them and returned, but did not try to
> > re-register the kobjects with the kobj core.
> >
> > In (b), the pci hotplug core allowed you to create multiple slots
> > with the same name, and called pci_create_slot() multiple times.
> > This time, since you were trying to create new slot objects, we
> > did not refcount them; we actually did a kzalloc *and* tried to
> > register them with the kobject core, which is why we got that
> > stack trace.
> >
> > I read your patch (a86161b3134465f) in closer detail and decided
> > that it can work without problems with my patch series.
> >
> > - Your patch will keep track of hotplug slots and
> > disallow multiple hotplug slots with the same name
> >
> > - the PCI slot infrastructure will still allow multiple
> > callers of pci_create_slot() to succeed by refcounting
> > identical slots
> >
> > This is the correct behavior to allow pciehp and pci_slot to
> > coexist because pci_slot is not trying to register a hotplug
> > handler or do any other hotplug operations.
> >
>
> Thank you for explanation. I understood.
>
> But I have one concern about the behavior when pci slot driver is not
> loaded. My patch (a86161b3134465f) prevents the kernel trace dump
> because of duplicate kobject add that would happen in the following two
> cases, though (b) is not described in the header of the patch (sorry).
>
> (a) multiple driver attempt to handle the same slot.
>
> (b) one or more driver attempt to register multiple slots with the
> same name (This can happen if broken platform assigns the same
> slot number to multiple hotplug slots, for example).
>
> With your patch, duplicate kobject add in case (b) is not prevented.
> That is my concern.
I apologize, I did not explain well enough. Let me try again.
After reading through your patch a86161b3134465f, I agree that we
should keep the functionality and the code. The refreshed patch
series I sent out yesterday (v15) includes your commit.
Here is the fully patched version of pci_hp_register, after
applying all 3 of my patches:
int pci_hp_register(struct hotplug_slot *slot, struct pci_bus *bus, int slot_nr)
{
int result;
struct pci_slot *pci_slot;
struct hotplug_slot *tmp;
if (slot == NULL)
return -ENODEV;
if ((slot->info == NULL) || (slot->ops == NULL))
return -EINVAL;
if (slot->release == NULL) {
dbg("Why are you trying to register a hotplug slot "
"without a proper release function?\n");
return -EINVAL;
}
/* Check if we have already registered a slot with the same name. */
tmp = get_slot_from_name(slot->name);
if (tmp)
return -EEXIST;
/*
* No problems if we call this interface from both ACPI_PCI_SLOT
* driver and call it here again. If we've already created the
* pci_slot, the interface will simply bump the refcount.
*/
pci_slot = pci_create_slot(bus, slot_nr, slot->name);
[...]
Note how we're checking get_slot_from_name. That should prevent
your scenario (b) that you describe above.
Maybe the diff was confusing, but I am definitely not removing
your code. I'm simply adding on top of a86161b3134465f, and not
removing it.
> I made a below patch to prevent (b), please take a look. And could you
> please consider merging it to "[PATCH 2/3] Introduce pci_slot" in your
> latest series.
Ok, now this is very confusing to me. Why is this patch so
different from a86161b3134465f?
Are you saying the call to get_slot_from_name() is no longer
sufficient?
Thanks,
/ac
>
> Thanks,
> Kenji Kaneshige
>
>
> ---
> drivers/pci/hotplug/pci_hotplug_core.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> Index: 20080610/drivers/pci/hotplug/pci_hotplug_core.c
> ===================================================================
> --- 20080610.orig/drivers/pci/hotplug/pci_hotplug_core.c
> +++ 20080610/drivers/pci/hotplug/pci_hotplug_core.c
> @@ -555,6 +555,7 @@ int pci_hp_register(struct hotplug_slot
> {
> int result;
> struct pci_slot *pci_slot;
> + struct hotplug_slot *tmp;
>
> if (slot == NULL)
> return -ENODEV;
> @@ -567,6 +568,21 @@ int pci_hp_register(struct hotplug_slot
> }
>
> /*
> + * Prevent registering multiple hotplug slots with the same name.
> + */
> + spin_lock(&pci_hotplug_slot_list_lock);
> + list_for_each_entry(tmp, &pci_hotplug_slot_list, slot_list) {
> + pci_slot = tmp->pci_slot;
> + if (pci_slot->bus == bus && pci_slot->number == slot_nr)
> + continue;
> + if (!strcmp(tmp->name, slot->name)) {
> + spin_unlock(&pci_hotplug_slot_list_lock);
> + return -EEXIST;
> + }
> + }
> + spin_unlock(&pci_hotplug_slot_list_lock);
> +
> + /*
> * No problems if we call this interface from both ACPI_PCI_SLOT
> * driver and call it here again. If we've already created the
> * pci_slot, the interface will simply bump the refcount.
>
>
--
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