On Thu, Apr 25, 2024 at 05:51:38PM -0500, Bjorn Helgaas wrote:
> On Thu, Apr 18, 2024 at 06:53:02PM -0700, Dexuan Cui wrote:
> > There has been an effort to make the pci-hyperv driver support
> > async-probing to reduce the boot time. With async-probing, multiple
> > kernel threads can be running hv_pci_probe() -> create_root_hv_pci_bus() ->
> > pci_scan_root_bus_bridge() -> pci_bus_insert_busn_res() at the same time to
> > update the global list, causing list corruption.
> >
> > Add a mutex to protect the list.
>
> I think it's a good idea to support probing multiple PCI root buses in
> parallel.
>
> The problem in get_pci_domain_busn_res() is the global
> pci_domain_busn_res_list. I'm not even sure what that list contains,
> since it's a lookup by "domain_nr". In the hv case, you probably have
> one host bridge per domain, but in general there may be multiple root
> buses in the same domain, e.g.,
>
> ACPI: PCI Root Bridge [PC00] (domain 0000 [bus 00-16])
> ACPI: PCI Root Bridge [PC01] (domain 0000 [bus 17-39])
> ACPI: PCI Root Bridge [PC02] (domain 0000 [bus 3a-5c])
> ...
>
> We only use get_pci_domain_busn_res() for root buses, and we should
> know the bus number range for root buses when we set up the struct
> pci_host_bridge, so it seems like we should keep the bus number
> resource there instead of allocating it in this sort of random place.
>
> Then we shouldn't need this weird pci_domain_busn_res_list at all.
Oops, sorry, I totally missed the point here. The point is that for
each domain, we get a new 00-ff range of possible bus numbers. This
is independent of the host bridges for that domain that may exist.
Then each host bridge will allocate a piece of the 00-ff range.
But I do still think get_pci_domain_busn_res() isn't really the best
place for this. It seems like it should be at a higher level,
connected somehow to domain number allocation, e.g., somewhere related
to bridge->domain_nr like the pci_bus_find_domain_nr() path.
> > Signed-off-by: Dexuan Cui <de...@microsoft.com>
> > ---
> > drivers/pci/probe.c | 25 ++++++++++++++++++-------
> > 1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index e19b79821dd6..1327fd820b24 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -37,6 +37,7 @@ LIST_HEAD(pci_root_buses);
> > EXPORT_SYMBOL(pci_root_buses);
> >
> > static LIST_HEAD(pci_domain_busn_res_list);
> > +static DEFINE_MUTEX(pci_domain_busn_res_list_lock);
> >
> > struct pci_domain_busn_res {
> > struct list_head list;
> > @@ -47,14 +48,22 @@ struct pci_domain_busn_res {
> > static struct resource *get_pci_domain_busn_res(int domain_nr)
> > {
> > struct pci_domain_busn_res *r;
> > + struct resource *ret;
> >
> > - list_for_each_entry(r, &pci_domain_busn_res_list, list)
> > - if (r->domain_nr == domain_nr)
> > - return &r->res;
> > + mutex_lock(&pci_domain_busn_res_list_lock);
> > +
> > + list_for_each_entry(r, &pci_domain_busn_res_list, list) {
> > + if (r->domain_nr == domain_nr) {
> > + ret = &r->res;
> > + goto out;
> > + }
> > + }
> >
> > r = kzalloc(sizeof(*r), GFP_KERNEL);
> > - if (!r)
> > - return NULL;
> > + if (!r) {
> > + ret = NULL;
> > + goto out;
> > + }
> >
> > r->domain_nr = domain_nr;
> > r->res.start = 0;
> > @@ -62,8 +71,10 @@ static struct resource *get_pci_domain_busn_res(int
> > domain_nr)
> > r->res.flags = IORESOURCE_BUS | IORESOURCE_PCI_FIXED;
> >
> > list_add_tail(&r->list, &pci_domain_busn_res_list);
> > -
> > - return &r->res;
> > + ret = &r->res;
> > +out:
> > + mutex_unlock(&pci_domain_busn_res_list_lock);
> > + return ret;
> > }
> >
> > /*
> > --
> > 2.25.1
> >
