On Thu, Dec 21, 2023 at 06:39:36PM +0900, Shin'ichiro Kawasaki wrote:
> p2sb_bar() unhides P2SB device to get resources from the device. It
> guards the operation by locking pci_rescan_remove_lock so that parallel
> rescans do not find the P2SB device. However, this lock causes deadlock
> when PCI bus rescan is triggered by /sys/bus/pci/rescan. The rescan
> locks pci_rescan_remove_lock and probes PCI devices. When PCI devices
> call p2sb_bar() during probe, it locks pci_rescan_remove_lock again.
> Hence the deadlock.
>
> To avoid the deadlock, do not lock pci_rescan_remove_lock in p2sb_bar().
> Instead, do the lock at fs_initcall. Introduce p2sb_cache_resources()
> for fs_initcall which gets and caches the P2SB resources. At p2sb_bar(),
> refer the cache and return to the caller.
Thank you for the update!
My comments below.
...
> +/*
> + * Cache BAR0 of P2SB device functions 0 to 7
> + * TODO: Move this definition to pci.h together with same other definitions
Missing periods at the end of sentences.
> + */
> +#define NR_P2SB_RES_CACHE 8
...
> +static bool p2sb_valid_resource(struct resource *res)
> +{
> + return res->flags;
> +}
So, now if you look at this, there is no point in having the function.
But see below.
...
> + if (!p2sb_valid_resource(pci_resource_n(pdev, 0)))
> + return -ENOENT;
As per above (i.e. see below).
...
> + ret = p2sb_scan_and_cache_devfn(bus, devfn);
> + if (ret || PCI_FUNC(devfn) != 0)
> + return ret;
This hides the fact that we don't scan functions if P2SB is not 0.
if (ret)
return ret;
/* ...add a comment like above... */
if (PCI_FUNC(devfn) != 0)
return 0;
> + /*
> + * When function number of the P2SB device is zero, scan other function
The first part will become the comment above. So, you may drop it from here.
> + * numbers. If devices are available, cache their BAR0.
> + */
...
> + pci_bus_write_config_dword(p2sb_bus, devfn_p2sb, P2SBC,
> + P2SBC_HIDE);
Having it on one line is fine.
...
> + if (!bus)
> + bus = p2sb_bus;
Hmm... Maybe
static struct pci_bus *p2sb_get_bus(bus)
{
static struct pci_bus *p2sb_bus;
bus = bus ?: p2sb_bus;
if (bus)
return bus;
p2sb_bus = ...;
return p2sb_bus;
}
?
...
> + if (!devfn) {
Maybe move this check to the callee?
> + ret = p2sb_get_devfn(&devfn);
> + if (ret)
> + return ret;
> + }
...
> + cache = &p2sb_resources[PCI_FUNC(devfn)];
> + if (!p2sb_valid_resource(&cache->res) ||
> + cache->bus_dev_id != bus->dev.id)
> return -ENODEV;
I don't remember if I mentioned in the last email(s), but I think what you want is
static int p2sb_valid_resource(struct resource *res)
{
return res->flags ? 0 : -ENOENT;
}
...
cache = &p2sb_resources[PCI_FUNC(devfn)];
if (cache->bus_dev_id != bus->dev.id)
return -ENODEV;
ret = p2sb_valid_resource(&cache->res);
if (ret)
return ret;
--
With Best Regards,
Andy Shevchenko
