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. Changes from RFC v2: * Reflected review comments on the list * Removed RFC prefix Changes from RFC v1: * Fixed a build warning poitned out in llvm list by kernel test robot drivers/platform/x86/p2sb.c | 157 +++++++++++++++++++++++++----------- 1 file changed, 112 insertions(+), 45 deletions(-) diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c index 1cf2471d54dd..faf4c3c7abb0 100644 --- a/drivers/platform/x86/p2sb.c +++ b/drivers/platform/x86/p2sb.c @@ -26,6 +26,20 @@ static const struct x86_cpu_id p2sb_cpu_ids[] = { {} }; +/* + * Cache BAR0 of P2SB device functions 0 to 7 + * TODO: Move this definition to pci.h together with same other definitions + */ +#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 struct pci_bus *p2sb_bus; + static int p2sb_get_devfn(unsigned int *devfn) { unsigned int fn = P2SB_DEVFN_DEFAULT; @@ -39,10 +53,15 @@ static int p2sb_get_devfn(unsigned int *devfn) return 0; } +static bool p2sb_valid_resource(struct resource *res) +{ + return res->flags; +} + /* 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]; + struct resource *bar0 = pci_resource_n(pdev, 0); /* Make sure we have no dangling pointers in the output */ memset(mem, 0, sizeof(*mem)); @@ -56,47 +75,50 @@ 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_devfn(struct pci_bus *bus, unsigned int devfn) { + struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)]; struct pci_dev *pdev; - int ret; pdev = pci_scan_single_device(bus, devfn); if (!pdev) return -ENODEV; - ret = p2sb_read_bar0(pdev, mem); + if (!p2sb_valid_resource(pci_resource_n(pdev, 0))) + return -ENOENT; + + p2sb_read_bar0(pdev, &cache->res); + cache->bus_dev_id = bus->dev.id; pci_stop_and_remove_bus_device(pdev); - return ret; + 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 - * - * 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_scan_and_cache(struct pci_bus *bus, unsigned int devfn) +{ + unsigned int slot, fn; + int ret; + + /* Scan the P2SB device and cache its BAR0 */ + ret = p2sb_scan_and_cache_devfn(bus, devfn); + if (ret || PCI_FUNC(devfn) != 0) + return ret; + + /* + * When function number of the P2SB device is zero, scan other function + * numbers. If devices are available, cache their BAR0. + */ + slot = PCI_SLOT(devfn); + for (fn = 1; fn < NR_P2SB_RES_CACHE; fn++) + p2sb_scan_and_cache_devfn(bus, PCI_DEVFN(slot, fn)); + + return 0; +} + +static int p2sb_cache_resources(void) { - struct pci_dev *pdev_p2sb; unsigned int devfn_p2sb; u32 value = P2SBC_HIDE; int ret; @@ -106,8 +128,8 @@ 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 */ + p2sb_bus = pci_find_bus(0, 0); /* * Prevent concurrent PCI bus scan from seeing the P2SB device and @@ -115,30 +137,75 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem) */ pci_lock_rescan_remove(); - /* Unhide the P2SB device, if needed */ - pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value); + /* + * 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(p2sb_bus, devfn_p2sb, P2SBC, &value); if (value & P2SBC_HIDE) - pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0); + pci_bus_write_config_dword(p2sb_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); + ret = p2sb_scan_and_cache(p2sb_bus, devfn_p2sb); /* Hide the P2SB device, if it was hidden */ if (value & P2SBC_HIDE) - pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE); - + pci_bus_write_config_dword(p2sb_bus, devfn_p2sb, P2SBC, + P2SBC_HIDE); pci_unlock_rescan_remove(); - if (ret) - return ret; + return ret; +} - if (mem->flags == 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) +{ + struct p2sb_res_cache *cache; + int ret; + + if (!bus) + bus = p2sb_bus; + + if (!devfn) { + 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; + 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; +} + +/* + * pci_rescan_remove_lock avoids access to unhidden P2SB devices, but it causes + * deadlock with sysfs pci bus rescan. To avoid the deadlock, access to P2SB + * devices at an early step in kernel initialization and cache required + * resources. This should happen after subsys_initcall which initializes PCI + * subsystem and before device_initcall which requires P2SB resources. + */ +fs_initcall(p2sb_fs_init); -- 2.43.0
