[PATCH 6.6-stable 1/2] PCI: Introduce cleanup helpers for device reference counts and locks
From: Ira Weiny ira.weiny@intel.com
commit ced085ef369af7a2b6da962ec2fbd01339f60693 upstream.
The "goto error" pattern is notorious for introducing subtle resource leaks. Use the new cleanup.h helpers for PCI device reference counts and locks.
Similar to the new put_device() and device_lock() cleanup helpers, __free(put_device) and guard(device), define the same for PCI devices, __free(pci_dev_put) and guard(pci_dev). These helpers eliminate the need for "goto free;" and "goto unlock;" patterns. For example, A 'struct pci_dev *' instance declared as:
struct pci_dev *pdev __free(pci_dev_put) = NULL;
...will automatically call pci_dev_put() if @pdev is non-NULL when @pdev goes out of scope (automatic variable scope). If a function wants to invoke pci_dev_put() on error, but return @pdev on success, it can do:
return no_free_ptr(pdev);
...or:
return_ptr(pdev);
For potential cleanup opportunity there are 587 open-coded calls to pci_dev_put() in the kernel with 65 instances within 10 lines of a goto statement with the CXL driver threatening to add another one.
The guard() helper holds the associated lock for the remainder of the current scope in which it was invoked. So, for example:
func(...) { if (...) { ... guard(pci_dev); /* pci_dev_lock() invoked here */ ... } /* <- implied pci_dev_unlock() triggered here */ }
There are 15 invocations of pci_dev_unlock() in the kernel with 5 instances within 10 lines of a goto statement. Again, the CXL driver is threatening to add another.
Introduce these helpers to preclude the addition of new more error prone goto put; / goto unlock; sequences. For now, these helpers are used in drivers/cxl/pci.c to allow ACPI error reports to be fed back into the CXL driver associated with the PCI device identified in the report.
Cc: Bjorn Helgaas bhelgaas@google.com Signed-off-by: Ira Weiny ira.weiny@intel.com Link: https://lore.kernel.org/r/20231220-cxl-cper-v5-8-1bb8a4ca2c7a@intel.com [djbw: rewrite changelog] Acked-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Jonathan Cameron Jonathan.Cameron@huawei.com Acked-by: Ard Biesheuvel ardb@kernel.org Signed-off-by: Dan Williams dan.j.williams@intel.com Signed-off-by: Lukas Wunner lukas@wunner.de --- include/linux/pci.h | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/include/linux/pci.h b/include/linux/pci.h index 512cb40150df..f14130011621 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1146,6 +1146,7 @@ int pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge); u8 pci_common_swizzle(struct pci_dev *dev, u8 *pinp); struct pci_dev *pci_dev_get(struct pci_dev *dev); void pci_dev_put(struct pci_dev *dev); +DEFINE_FREE(pci_dev_put, struct pci_dev *, if (_T) pci_dev_put(_T)) void pci_remove_bus(struct pci_bus *b); void pci_stop_and_remove_bus_device(struct pci_dev *dev); void pci_stop_and_remove_bus_device_locked(struct pci_dev *dev); @@ -1851,6 +1852,7 @@ void pci_cfg_access_unlock(struct pci_dev *dev); void pci_dev_lock(struct pci_dev *dev); int pci_dev_trylock(struct pci_dev *dev); void pci_dev_unlock(struct pci_dev *dev); +DEFINE_GUARD(pci_dev, struct pci_dev *, pci_dev_lock(_T), pci_dev_unlock(_T))
/* * PCI domain support. Sometimes called PCI segment (eg by ACPI),
commit 11a1f4bc47362700fcbde717292158873fb847ed upstream.
Keith reports a use-after-free when a DPC event occurs concurrently to hot-removal of the same portion of the hierarchy:
The dpc_handler() awaits readiness of the secondary bus below the Downstream Port where the DPC event occurred. To do so, it polls the config space of the first child device on the secondary bus. If that child device is concurrently removed, accesses to its struct pci_dev cause the kernel to oops.
That's because pci_bridge_wait_for_secondary_bus() neglects to hold a reference on the child device. Before v6.3, the function was only called on resume from system sleep or on runtime resume. Holding a reference wasn't necessary back then because the pciehp IRQ thread could never run concurrently. (On resume from system sleep, IRQs are not enabled until after the resume_noirq phase. And runtime resume is always awaited before a PCI device is removed.)
However starting with v6.3, pci_bridge_wait_for_secondary_bus() is also called on a DPC event. Commit 53b54ad074de ("PCI/DPC: Await readiness of secondary bus after reset"), which introduced that, failed to appreciate that pci_bridge_wait_for_secondary_bus() now needs to hold a reference on the child device because dpc_handler() and pciehp may indeed run concurrently. The commit was backported to v5.10+ stable kernels, so that's the oldest one affected.
Add the missing reference acquisition.
Abridged stack trace:
BUG: unable to handle page fault for address: 00000000091400c0 CPU: 15 PID: 2464 Comm: irq/53-pcie-dpc 6.9.0 RIP: pci_bus_read_config_dword+0x17/0x50 pci_dev_wait() pci_bridge_wait_for_secondary_bus() dpc_reset_link() pcie_do_recovery() dpc_handler()
Fixes: 53b54ad074de ("PCI/DPC: Await readiness of secondary bus after reset") Closes: https://lore.kernel.org/r/20240612181625.3604512-3-kbusch@meta.com/ Link: https://lore.kernel.org/linux-pci/8e4bcd4116fd94f592f2bf2749f168099c480ddf.1... Reported-by: Keith Busch kbusch@kernel.org Tested-by: Keith Busch kbusch@kernel.org Signed-off-by: Lukas Wunner lukas@wunner.de Signed-off-by: Krzysztof Wilczyński kwilczynski@kernel.org Reviewed-by: Keith Busch kbusch@kernel.org Reviewed-by: Mika Westerberg mika.westerberg@linux.intel.com Cc: stable@vger.kernel.org # v5.10+ --- drivers/pci/pci.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index cd759e19cc18..a0f961a380fa 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -5123,7 +5123,7 @@ static int pci_bus_max_d3cold_delay(const struct pci_bus *bus) */ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type) { - struct pci_dev *child; + struct pci_dev *child __free(pci_dev_put) = NULL; int delay;
if (pci_dev_is_disconnected(dev)) @@ -5152,8 +5152,8 @@ int pci_bridge_wait_for_secondary_bus(struct pci_dev *dev, char *reset_type) return 0; }
- child = list_first_entry(&dev->subordinate->devices, struct pci_dev, - bus_list); + child = pci_dev_get(list_first_entry(&dev->subordinate->devices, + struct pci_dev, bus_list)); up_read(&pci_bus_sem);
/*
linux-stable-mirror@lists.linaro.org
-
Lukas Wunner