Hi, On 12/1/23 11:47, 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. > > Link: https://lore.kernel.org/linux-pci/6xb24fjmptxxn5js2fjrrddjae6twex5bjaftwqsuawuqqqydx@7cl3uik5ef6j/ > Suggested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx> > --- > This patch reflects discussions held at the Link tag. I confirmed this patch > fixes the problem using a system with i2c_i801 device, building i2c_i801 > module as both built-in and loadable. Reviews will be appreicated. Andy, you know this code best, can you review this patch please? Regards, Hans > > drivers/platform/x86/p2sb.c | 125 +++++++++++++++++++++++++----------- > 1 file changed, 87 insertions(+), 38 deletions(-) > > diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c > index 1cf2471d54dd..97e9b44f5f1a 100644 > --- a/drivers/platform/x86/p2sb.c > +++ b/drivers/platform/x86/p2sb.c > @@ -26,6 +26,16 @@ static const struct x86_cpu_id p2sb_cpu_ids[] = { > {} > }; > > +/* Cache BAR0 of P2SB device from function 0 ot 7 */ > +#define NR_P2SB_RES_CACHE 8 > + > +struct p2sb_res_cache { > + u32 bus_dev_id; > + struct resource res; > +}; > + > +static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE]; > + > static int p2sb_get_devfn(unsigned int *devfn) > { > unsigned int fn = P2SB_DEVFN_DEFAULT; > @@ -39,8 +49,13 @@ static int p2sb_get_devfn(unsigned int *devfn) > return 0; > } > > +static bool p2sb_invalid_resource(struct resource *res) > +{ > + return res->flags == 0; > +} > + > /* Copy resource from the first BAR of the device in question */ > -static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) > +static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) > { > struct resource *bar0 = &pdev->resource[0]; > > @@ -56,48 +71,29 @@ static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem) > mem->end = bar0->end; > mem->flags = bar0->flags; > mem->desc = bar0->desc; > - > - return 0; > } > > -static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > +static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn) > { > struct pci_dev *pdev; > int ret; > + struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)]; > > pdev = pci_scan_single_device(bus, devfn); > - if (!pdev) > + if (!pdev || p2sb_invalid_resource(&pdev->resource[0])) > return -ENODEV; > > - ret = p2sb_read_bar0(pdev, mem); > + p2sb_read_bar0(pdev, &cache->res); > + cache->bus_dev_id = bus->dev.id; > > pci_stop_and_remove_bus_device(pdev); > return ret; > } > > -/** > - * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR > - * @bus: PCI bus to communicate with > - * @devfn: PCI slot and function to communicate with > - * @mem: memory resource to be filled in > - * > - * The BIOS prevents the P2SB device from being enumerated by the PCI > - * subsystem, so we need to unhide and hide it back to lookup the BAR. > - * > - * if @bus is NULL, the bus 0 in domain 0 will be used. > - * If @devfn is 0, it will be replaced by devfn of the P2SB device. > - * > - * Caller must provide a valid pointer to @mem. > - * > - * Locking is handled by pci_rescan_remove_lock mutex. > - * > - * Return: > - * 0 on success or appropriate errno value on error. > - */ > -int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > +static int p2sb_cache_resources(void) > { > - struct pci_dev *pdev_p2sb; > - unsigned int devfn_p2sb; > + struct pci_bus *bus; > + unsigned int devfn_p2sb, slot_p2sb, fn; > u32 value = P2SBC_HIDE; > int ret; > > @@ -106,8 +102,8 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > if (ret) > return ret; > > - /* if @bus is NULL, use bus 0 in domain 0 */ > - bus = bus ?: pci_find_bus(0, 0); > + /* Assume P2SB is on the bus 0 in domain 0 */ > + bus = pci_find_bus(0, 0); > > /* > * Prevent concurrent PCI bus scan from seeing the P2SB device and > @@ -115,18 +111,31 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > */ > pci_lock_rescan_remove(); > > - /* Unhide the P2SB device, if needed */ > + /* > + * The BIOS prevents the P2SB device from being enumerated by the PCI > + * subsystem, so we need to unhide and hide it back to lookup the BAR. > + * Unhide the P2SB device here, if needed. > + */ > pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value); > if (value & P2SBC_HIDE) > pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0); > > - pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb); > - if (devfn) > - ret = p2sb_scan_and_read(bus, devfn, mem); > - else > - ret = p2sb_read_bar0(pdev_p2sb, mem); > - pci_stop_and_remove_bus_device(pdev_p2sb); > + /* Scan the P2SB device and cache its BAR0 */ > + ret = p2sb_scan_and_cache(bus, devfn_p2sb); > + if (ret) > + goto out; > > + /* > + * When function number of the P2SB device is zero, scan other function > + * numbers. If devices are available, cache their BAR0. > + */ > + if (!PCI_FUNC(devfn_p2sb)) { > + slot_p2sb = PCI_SLOT(devfn_p2sb); > + for (fn = 1; fn < 8; fn++) > + p2sb_scan_and_cache(bus, PCI_DEVFN(slot_p2sb, fn)); > + } > + > +out: > /* Hide the P2SB device, if it was hidden */ > if (value & P2SBC_HIDE) > pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE); > @@ -136,9 +145,49 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > if (ret) > return ret; > > - if (mem->flags == 0) > + return 0; > +} > + > +/** > + * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR > + * @bus: PCI bus to communicate with > + * @devfn: PCI slot and function to communicate with > + * @mem: memory resource to be filled in > + * > + * if @bus is NULL, the bus 0 in domain 0 will be used. > + * If @devfn is 0, it will be replaced by devfn of the P2SB device. > + * > + * Caller must provide a valid pointer to @mem. > + * > + * Return: > + * 0 on success or appropriate errno value on error. > + */ > +int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) > +{ > + int ret; > + struct p2sb_res_cache *cache; > + > + bus = bus ? bus : pci_find_bus(0, 0); > + > + if (!devfn) { > + ret = p2sb_get_devfn(&devfn); > + if (ret) > + return ret; > + } > + > + cache = &p2sb_resources[PCI_FUNC(devfn)]; > + if (p2sb_invalid_resource(&cache->res) || > + cache->bus_dev_id != bus->dev.id) > return -ENODEV; > > + memcpy(mem, &cache->res, sizeof(*mem)); > return 0; > } > EXPORT_SYMBOL_GPL(p2sb_bar); > + > +static int __init p2sb_fs_init(void) > +{ > + p2sb_cache_resources(); > + return 0; > +} > +fs_initcall(p2sb_fs_init);
