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Lukas Wunner 24adef4f4f PCI/ACPI: Fix runtime PM ref imbalance on Hot-Plug Capable ports 
[ Upstream commit 6cff20ce3b ]

pci_bridge_d3_possible() is called from both pcie_portdrv_probe() and
pcie_portdrv_remove() to determine whether runtime power management shall
be enabled (on probe) or disabled (on remove) on a PCIe port.

The underlying assumption is that pci_bridge_d3_possible() always returns
the same value, else a runtime PM reference imbalance would occur.  That
assumption is not given if the PCIe port is inaccessible on remove due to
hot-unplug:  pci_bridge_d3_possible() calls pciehp_is_native(), which
accesses Config Space to determine whether the port is Hot-Plug Capable.
An inaccessible port returns "all ones", which is converted to "all
zeroes" by pcie_capability_read_dword().  Hence the port no longer seems
Hot-Plug Capable on remove even though it was on probe.

The resulting runtime PM ref imbalance causes warning messages such as:

  pcieport 0000:02:04.0: Runtime PM usage count underflow!

Avoid the Config Space access (and thus the runtime PM ref imbalance) by
caching the Hot-Plug Capable bit in struct pci_dev.

The struct already contains an "is_hotplug_bridge" flag, which however is
not only set on Hot-Plug Capable PCIe ports, but also Conventional PCI
Hot-Plug bridges and ACPI slots.  The flag identifies bridges which are
allocated additional MMIO and bus number resources to allow for hierarchy
expansion.

The kernel is somewhat sloppily using "is_hotplug_bridge" in a number of
places to identify Hot-Plug Capable PCIe ports, even though the flag
encompasses other devices.  Subsequent commits replace these occurrences
with the new flag to clearly delineate Hot-Plug Capable PCIe ports from
other kinds of hotplug bridges.

Document the existing "is_hotplug_bridge" and the new "is_pciehp" flag
and document the (non-obvious) requirement that pci_bridge_d3_possible()
always returns the same value across the entire lifetime of a bridge,
including its hot-removal.

Fixes: 5352a44a56 ("PCI: pciehp: Make pciehp_is_native() stricter")
Reported-by: Laurent Bigonville <bigon@bigon.be>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220216
Reported-by: Mario Limonciello <mario.limonciello@amd.com>
Closes: https://lore.kernel.org/r/20250609020223.269407-3-superm1@kernel.org/
Link: https://lore.kernel.org/all/20250620025535.3425049-3-superm1@kernel.org/T/#u
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Cc: stable@vger.kernel.org # v4.18+
Link: https://patch.msgid.link/fe5dcc3b2e62ee1df7905d746bde161eb1b3291c.1752390101.git.lukas@wunner.de
[ changed "recent enough PCIe ports" comment to "some PCIe ports" ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-08-28 16:26:10 +02:00
arch arm64/entry: Mask DAIF in cpu_switch_to(), call_on_irq_stack() 2025-08-28 16:26:10 +02:00
block block: reject invalid operation in submit_bio_noacct 2025-08-28 16:26:10 +02:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2025-04-25 10:44:04 +02:00
crypto crypto: xts - Only add ecb if it is not already there 2025-06-27 11:07:06 +01:00
Documentation dt-bindings: display: sprd,sharkl3-dsi-host: Fix missing clocks constraints 2025-08-28 16:26:06 +02:00
drivers PCI/ACPI: Fix runtime PM ref imbalance on Hot-Plug Capable ports 2025-08-28 16:26:10 +02:00
fs fscrypt: Don't use problematic non-inline crypto engines 2025-08-28 16:26:10 +02:00
include PCI/ACPI: Fix runtime PM ref imbalance on Hot-Plug Capable ports 2025-08-28 16:26:10 +02:00
init sched/isolation: Make CONFIG_CPU_ISOLATION depend on CONFIG_SMP 2025-05-02 07:47:04 +02:00
io_uring io_uring/poll: fix POLLERR handling 2025-07-24 08:51:48 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:07:30 +01:00
kernel module: Prevent silent truncation of module name in delete_module(2) 2025-08-28 16:26:01 +02:00
lib maple_tree: fix mt_destroy_walk() on root leaf node 2025-07-17 18:32:09 +02:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/kmemleak: avoid deadlock by moving pr_warn() outside kmemleak_lock 2025-08-28 16:26:04 +02:00
net net: add netdev_lockdep_set_classes() to virtual drivers 2025-08-28 16:26:10 +02:00
rust rust: module: place cleanup_module() in .exit.text section 2025-07-06 10:57:54 +02:00
samples samples: mei: Fix building on musl libc 2025-08-15 12:04:55 +02:00
scripts kconfig: lxdialog: fix 'space' to (de)select options 2025-08-28 16:26:02 +02:00
security apparmor: use the condition in AA_BUG_FMT even with debug disabled 2025-08-28 16:26:01 +02:00
sound ASoC: fsl_sai: replace regmap_write with regmap_update_bits 2025-08-28 16:26:03 +02:00
tools tools/nolibc: fix spelling of FD_SETBITMASK in FD_* macros 2025-08-28 16:26:04 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:07:25 +01:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:21:15 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS sign-file,extract-cert: move common SSL helper functions to a header 2025-04-25 10:44:04 +02:00
Makefile Linux 6.1.148 2025-08-15 12:05:13 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.