[PATCH v5 00/23] PCI: Convert all dynamic sysfs attributes to static

Krzysztof Wilczyński
2026-04-16T18:01:17Z

Hello,

This series converts every dynamically allocated PCI sysfs attribute to
a static const definition. After the full series, pci_sysfs_init() and
sysfs_initialized are gone, and every sysfs file is created by the
driver model at device_add() time.

Currently, the PCI resource files (resourceN, resourceN_wc) and the
legacy bus files (legacy_io, legacy_mem) are created dynamically
from two unsynchronised paths:

Path A: late_initcall

pci_sysfs_init (late_initcall)
sysfs_initialized = 1
for_each_pci_dev
pci_create_sysfs_dev_files
sysfs_create_bin_file (resourceN, resourceN_wc)
pci_find_next_bus
pci_create_legacy_files
sysfs_create_bin_file (legacy_io, legacy_mem)

Path B: device registration / hotplug

pci_bus_add_devices
pci_bus_add_device
pci_create_sysfs_dev_files
if (!sysfs_initialized) return <- only guard
sysfs_create_bin_file (resourceN, resourceN_wc)

On most ACPI systems this does not race because PCI enumeration
completes at subsys_initcall time, before pci_sysfs_init() runs:

subsys_initcall (level 4):
acpi_pci_root_add
pci_bus_add_device
pci_create_sysfs_dev_files
if (!sysfs_initialized) <- not yet set
return -EACCES

late_initcall (level 7):
pci_sysfs_init
sysfs_initialized = 1
for_each_pci_dev
pci_create_sysfs_dev_files <- creates the files, no race

On Devicetree platforms the host controller is a platform driver that
probes via the driver model, often on a workqueue, and overlaps with the
late_initcall:

CPU 0 (late_initcall) CPU 1 (driver probe)
--------------------------- ----------------------------
pci_sysfs_init()
sysfs_initialized = 1
for_each_pci_dev(pdev) pci_bus_add_device(pdev)
pci_create_sysfs_dev_files() pci_create_sysfs_dev_files()
sysfs_create_bin_file() sysfs_create_bin_file()
-> "duplicate filename"

The same happens on ACPI when probing is asynchronous (hv_pci on
Azure, RISC-V with ACPI).

The duplicate causes sysfs_create_bin_file() to fail with -EEXIST.
pci_create_resource_files() then calls pci_remove_resource_files() in
its error unwind, tearing down files the other thread created and
still references through pdev->res_attr[]. This has caused kernel
panics on i.MX6 and boot failures on other platforms.

Several different fixes have been proposed over the years: reordering
the sysfs_initialized assignment, adding locks, checking
pci_dev_is_added(), setting pdev->res_attr[] to NULL after kfree
(which only prevents a double-free on the teardown path, not the
error unwind removing the other thread's files). None would address the
root cause.

This has been reported a few times:

- https://lore.kernel.org/linux-pci/20250702155112.40124-1-heshuan@bytedance.com/
- https://lore.kernel.org/linux-pci/b51519d6-ce45-4b6d-8135-c70169bd110e@h-partners.com/
- https://lore.kernel.org/linux-pci/1702093576-30405-1-git-send-email-ssengar@linux.microsoft.com/
- https://lore.kernel.org/linux-pci/SY0P300MB04687548090B73E40AF97D8897B82@SY0P300MB0468.AUSP300.PROD.OUTLOOK.COM/
- https://lore.kernel.org/linux-pci/20230105174736.GA1154719@bhelgaas/
- https://lore.kernel.org/linux-pci/m3eebg9puj.fsf@t19.piap.pl/
- https://lore.kernel.org/linux-pci/20200716110423.xtfyb3n6tn5ixedh@pali/
- https://lore.kernel.org/linux-pci/1366196798-15929-1-git-send-email-artem.savkov@gmail.com/
- https://bugzilla.kernel.org/show_bug.cgi?id=215515
- https://bugzilla.kernel.org/show_bug.cgi?id=216888

With static attributes the driver model creates sysfs entries once per
device at device_add() time, under the device lock, eliminating the
late_initcall iteration and the race along with it.

Krzysztof

---
Changes in v5:
https://lore.kernel.org/linux-pci/20260411080148.471335-1-kwilczynski@kernel.org/

- Added new Tested-by, Reviewed-by, and Acked-by tags.
- Used the existing _io function names in the static macro
definitions, deferring the rename to the conversion commit
where it belongs, to avoid a forward reference across
commits. This was reported by Sashiko, see:
https://sashiko.dev/#/patchset/20260411080148.471335-1-kwilczynski%40kernel.org?part=6
- Folded the __resource_resize_store() conversion into the
main static attributes commit so the resize path is never
broken between commits. This was reported by Sashiko, see:
https://sashiko.dev/#/patchset/20260410055040.39233-1-kwilczynski%40kernel.org?part=6
https://sashiko.dev/#/patchset/20260411080148.471335-1-kwilczynski%40kernel.org?part=7
- Dropped the unnecessary parentheses cleanup from the Alpha
BAR index commit, as the line is replaced two commits later
anyway, as per Ilpo Järvinen's feedback.
- Squashed the Alpha accessor macro and cleanup commits into
one, using pci_resource_is_mem() directly instead of the
intermediate pci_resource_flags() step, as per Ilpo
Järvinen's feedback.
- Moved the raw literal conversion in pci_create_legacy_files()
into the macro definition commit, so the macros and their
usage are introduced together, as per Ilpo Järvinen's
feedback.
- Removed unnecessary backslash line continuation from the
ternary in pci_mmap_legacy_page_range().
- Kept pci_resource_len() for visibility checks instead of
resource_assigned(). The static is_visible() callback
runs at device_add() time during the PCI enumeration,
before the pci_assign_unassigned_bus_resources() populates
res->parent, as such, resource_assigned() returned false
for every BAR, hiding all resource files. This is related
to review feedback from Ilpo Järvinen.

Changes in v4:
https://lore.kernel.org/linux-pci/20260410055040.39233-1-kwilczynski@kernel.org/

- Added new Reviewed-by tags.
- Added pci_resource_is_io() and pci_resource_is_mem() helpers
for resource type checks, replacing the open-coded bitwise
flag tests in pci_mmap_resource(), pci_resource_io(), and
Alpha's pci_mmap_resource(), as per Ilpo Järvinen's
suggestion.
- Split the __pci_mmap_fits() cleanup into two patches. An
overflow fix for zero-length BARs, which now includes a
Fixes: tag referencing the original Alpha PCI sysfs commit,
and the WARN macro removal is a separate cleanup as per Ilpo
Järvinen's suggestion.
- Added a missing Fixes: tag to the Alpha lockdown check,
referencing the commit that added the check to the generic
path but missed Alpha's implementation.
- Added PCI_LEGACY_IO_SIZE and PCI_LEGACY_MEM_SIZE macros to
replace the raw literals used for legacy address space sizes.
These are used in both Alpha's pci_mmap_legacy_page_range()
and the static legacy attribute definitions, as per Ilpo
Järvinen's suggestion.
- Replaced sysfs_update_groups() in the BAR resize path with
sysfs_remove_groups() before the resize and sysfs_create_groups()
after, restoring the original teardown before BAR resize
ordering. This was reported by Sashiko, see:
https://sashiko.dev/#/patchset/20260410055040.39233-1-kwilczynski%40kernel.org?part=7
- Defined pci_dev_resource_attr_groups as a NULL macro when
HAVE_PCI_MMAP and ARCH_GENERIC_PCI_MMAP_RESOURCE are both
absent, so the resize path compiles unconditionally without
#ifdef guards in the function body. This was reported by
Sashiko, see:
https://sashiko.dev/#/patchset/20260410055040.39233-1-kwilczynski%40kernel.org?part=7
- Moved the pci_legacy_has_sparse() prototype into the patch
that introduces the function, alongside the existing
pci_adjust_legacy_attr() declaration, to fix a bisection
issue where Alpha would warn on -Wmissing-prototypes.
This was reported by Sashiko, see:
https://sashiko.dev/#/patchset/20260410055040.39233-1-kwilczynski%40kernel.org?part=18

Changes in v3:
https://lore.kernel.org/linux-pci/20210910202623.2293708-1-kw@linux.com/

- Updated for modern kernel releases and expanded scope. The
v2 only covered the generic resource files. This version
also converts Alpha's sparse/dense resource files and the
legacy bus attributes, removing pci_sysfs_init() entirely.
- Split the single macro definition into three distinct ones
(per I/O, UC, and WC), to make sure that each carries only
the callbacks its resource type needs.
- Updated to use the new .bin_size callback, as the attributes
are const, to replace using a->size directly, which was not
ideal. This required changes to pci_llseek_resource(), to
ensure that it would work for device and bus-level attributes.
- Updated the __resource_resize_store() to include CAP_SYS_ADMIN
capabilities check.
- Added the security_locked_down() check to Alpha's
pci_mmap_resource(), to align with other architectures.

Changes in v2:
https://lore.kernel.org/linux-pci/20210825212255.878043-1-kw@linux.com/

- Refactored code so that the macros, helpers and internal
functions can be used to correctly leverage the read(),
write() and mmap() callbacks rather than to use the
.is_bin_visible() callback to set up sysfs objects
internals as this is not supported.
- Refactored some if-statements to check for a resource
flag first, and then call either arch_can_pci_mmap_io()
or arch_can_pci_mmap_wc(), plus store result of testing
for IORESOURCE_MEM and IORESOURCE_PREFETCH flags into
a boolean variable, as per Bjorn Helgaas' suggestion.
- Renamed pci_read_resource_io() and pci_write_resource_io()
callbacks so that these are not specifically tied to I/O
BARs read() and write() operations also as per Bjorn
Helgaas' suggestion.
- Updated style for code handling bitwise operations to
match the style that is preferred as per Bjorn Helgaas'
suggestion.
- Updated commit messages adding more details about the
implementation as requested by Bjorn Helgaas.

Krzysztof Wilczyński (23):
PCI/sysfs: Use PCI resource accessor macros
PCI: Add pci_resource_is_io() and pci_resource_is_mem() helpers
PCI/sysfs: Only allow supported resource types in I/O and MMIO helpers
PCI/sysfs: Use BAR length in pci_llseek_resource() when attr->size is
zero
PCI/sysfs: Add CAP_SYS_ADMIN check to __resource_resize_store()
PCI/sysfs: Add static PCI resource attribute macros
PCI/sysfs: Convert PCI resource files to static attributes
PCI/sysfs: Warn about BAR resize failure in __resource_resize_store()
PCI/sysfs: Add stubs for pci_{create,remove}_sysfs_dev_files()
PCI/sysfs: Limit pci_sysfs_init() late_initcall compile scope
alpha/PCI: Add security_locked_down() check to pci_mmap_resource()
alpha/PCI: Use BAR index in sysfs attr->private instead of resource
pointer
alpha/PCI: Use PCI resource accessor macros
alpha/PCI: Fix __pci_mmap_fits() overflow for zero-length BARs
alpha/PCI: Remove WARN from __pci_mmap_fits()
alpha/PCI: Add static PCI resource attribute macros
alpha/PCI: Convert resource files to static attributes
PCI/sysfs: Remove pci_{create,remove}_sysfs_dev_files()
PCI: Add macros for legacy I/O and memory address space sizes
alpha/PCI: Compute legacy size in pci_mmap_legacy_page_range()
PCI/sysfs: Add __weak pci_legacy_has_sparse() helper
PCI/sysfs: Convert legacy I/O and memory attributes to static
definitions
PCI/sysfs: Remove pci_create_legacy_files() and pci_sysfs_init()

arch/alpha/include/asm/pci.h | 13 +-
arch/alpha/kernel/pci-sysfs.c | 373 +++++++++++----------
arch/powerpc/include/asm/pci.h | 2 -
drivers/pci/bus.c | 1 -
drivers/pci/pci-sysfs.c | 575 +++++++++++++++++++--------------
drivers/pci/pci.h | 16 +-
drivers/pci/probe.c | 6 -
drivers/pci/remove.c | 3 -
include/linux/pci.h | 39 ++-
9 files changed, 578 insertions(+), 450 deletions(-)

--
2.53.0