The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x f5eff5591b8f9c5effd25c92c758a127765f74c1 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023050601-kimono-varsity-8905@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From f5eff5591b8f9c5effd25c92c758a127765f74c1 Mon Sep 17 00:00:00 2001 From: Lukas Wunner <lukas@xxxxxxxxx> Date: Tue, 11 Apr 2023 08:21:02 +0200 Subject: [PATCH] PCI: pciehp: Fix AB-BA deadlock between reset_lock and device_lock In 2013, commits 2e35afaefe64 ("PCI: pciehp: Add reset_slot() method") 608c388122c7 ("PCI: Add slot reset option to pci_dev_reset()") amended PCIe hotplug to mask Presence Detect Changed events during a Secondary Bus Reset. The reset thus no longer causes gratuitous slot bringdown and bringup. However the commits neglected to serialize reset with code paths reading slot registers. For instance, a slot bringup due to an earlier hotplug event may see the Presence Detect State bit cleared during a concurrent Secondary Bus Reset. In 2018, commit 5b3f7b7d062b ("PCI: pciehp: Avoid slot access during reset") retrofitted the missing locking. It introduced a reset_lock which serializes a Secondary Bus Reset with other parts of pciehp. Unfortunately the locking turns out to be overzealous: reset_lock is held for the entire enumeration and de-enumeration of hotplugged devices, including driver binding and unbinding. Driver binding and unbinding acquires device_lock while the reset_lock of the ancestral hotplug port is held. A concurrent Secondary Bus Reset acquires the ancestral reset_lock while already holding the device_lock. The asymmetric locking order in the two code paths can lead to AB-BA deadlocks. Michael Haeuptle reports such deadlocks on simultaneous hot-removal and vfio release (the latter implies a Secondary Bus Reset): pciehp_ist() # down_read(reset_lock) pciehp_handle_presence_or_link_change() pciehp_disable_slot() __pciehp_disable_slot() remove_board() pciehp_unconfigure_device() pci_stop_and_remove_bus_device() pci_stop_bus_device() pci_stop_dev() device_release_driver() device_release_driver_internal() __device_driver_lock() # device_lock() SYS_munmap() vfio_device_fops_release() vfio_device_group_close() vfio_device_close() vfio_device_last_close() vfio_pci_core_close_device() vfio_pci_core_disable() # device_lock() __pci_reset_function_locked() pci_reset_bus_function() pci_dev_reset_slot_function() pci_reset_hotplug_slot() pciehp_reset_slot() # down_write(reset_lock) Ian May reports the same deadlock on simultaneous hot-removal and an AER-induced Secondary Bus Reset: aer_recover_work_func() pcie_do_recovery() aer_root_reset() pci_bus_error_reset() pci_slot_reset() pci_slot_lock() # device_lock() pci_reset_hotplug_slot() pciehp_reset_slot() # down_write(reset_lock) Fix by releasing the reset_lock during driver binding and unbinding, thereby splitting and shrinking the critical section. Driver binding and unbinding is protected by the device_lock() and thus serialized with a Secondary Bus Reset. There's no need to additionally protect it with the reset_lock. However, pciehp does not bind and unbind devices directly, but rather invokes PCI core functions which also perform certain enumeration and de-enumeration steps. The reset_lock's purpose is to protect slot registers, not enumeration and de-enumeration of hotplugged devices. That would arguably be the job of the PCI core, not the PCIe hotplug driver. After all, an AER-induced Secondary Bus Reset may as well happen during boot-time enumeration of the PCI hierarchy and there's no locking to prevent that either. Exempting *de-enumeration* from the reset_lock is relatively harmless: A concurrent Secondary Bus Reset may foil config space accesses such as PME interrupt disablement. But if the device is physically gone, those accesses are pointless anyway. If the device is physically present and only logically removed through an Attention Button press or the sysfs "power" attribute, PME interrupts as well as DMA cannot come through because pciehp_unconfigure_device() disables INTx and Bus Master bits. That's still protected by the reset_lock in the present commit. Exempting *enumeration* from the reset_lock also has limited impact: The exempted call to pci_bus_add_device() may perform device accesses through pcibios_bus_add_device() and pci_fixup_device() which are now no longer protected from a concurrent Secondary Bus Reset. Otherwise there should be no impact. In essence, the present commit seeks to fix the AB-BA deadlocks while still retaining a best-effort reset protection for enumeration and de-enumeration of hotplugged devices -- until a general solution is implemented in the PCI core. Link: https://lore.kernel.org/linux-pci/CS1PR8401MB0728FC6FDAB8A35C22BD90EC95F10@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Link: https://lore.kernel.org/linux-pci/20200615143250.438252-1-ian.may@xxxxxxxxxxxxx Link: https://lore.kernel.org/linux-pci/ce878dab-c0c4-5bd0-a725-9805a075682d@xxxxxxx Link: https://lore.kernel.org/linux-pci/ed831249-384a-6d35-0831-70af191e9bce@xxxxxxxxxx Link: https://bugzilla.kernel.org/show_bug.cgi?id=215590 Fixes: 5b3f7b7d062b ("PCI: pciehp: Avoid slot access during reset") Link: https://lore.kernel.org/r/fef2b2e9edf245c049a8c5b94743c0f74ff5008a.1681191902.git.lukas@xxxxxxxxx Reported-by: Michael Haeuptle <michael.haeuptle@xxxxxxx> Reported-by: Ian May <ian.may@xxxxxxxxxxxxx> Reported-by: Andrey Grodzovsky <andrey2805@xxxxxxxxx> Reported-by: Rahul Kumar <rahul.kumar1@xxxxxxx> Reported-by: Jialin Zhang <zhangjialin11@xxxxxxxxxx> Tested-by: Anatoli Antonovitch <Anatoli.Antonovitch@xxxxxxx> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v4.19+ Cc: Dan Stein <dstein@xxxxxxx> Cc: Ashok Raj <ashok.raj@xxxxxxxxx> Cc: Alex Michon <amichon@xxxxxxxxxxxxx> Cc: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> Cc: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c index d17f3bf36f70..ad12515a4a12 100644 --- a/drivers/pci/hotplug/pciehp_pci.c +++ b/drivers/pci/hotplug/pciehp_pci.c @@ -63,7 +63,14 @@ int pciehp_configure_device(struct controller *ctrl) pci_assign_unassigned_bridge_resources(bridge); pcie_bus_configure_settings(parent); + + /* + * Release reset_lock during driver binding + * to avoid AB-BA deadlock with device_lock. + */ + up_read(&ctrl->reset_lock); pci_bus_add_devices(parent); + down_read_nested(&ctrl->reset_lock, ctrl->depth); out: pci_unlock_rescan_remove(); @@ -104,7 +111,15 @@ void pciehp_unconfigure_device(struct controller *ctrl, bool presence) list_for_each_entry_safe_reverse(dev, temp, &parent->devices, bus_list) { pci_dev_get(dev); + + /* + * Release reset_lock during driver unbinding + * to avoid AB-BA deadlock with device_lock. + */ + up_read(&ctrl->reset_lock); pci_stop_and_remove_bus_device(dev); + down_read_nested(&ctrl->reset_lock, ctrl->depth); + /* * Ensure that no new Requests will be generated from * the device.
