linux-stable.git/drivers/pci/hotplug/pci_hotplug_core.c, branch v6.15

PCI: hotplug: Inline pci_hp_{create,remove}_module_link()

2025-03-04T23:00:12+00:00

For no apparent reason, the pci_hp_{create,remove}_module_link() helpers
live in slot.c, even though they're only called from two functions in
pci_hotplug_core.c.

Inline the helpers to reduce code size and number of exported symbols.

Link: https://lore.kernel.org/r/c207f03cfe32ae9002d9b453001a1dd63d9ab3fb.1740501868.git.lukas@wunner.de
Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Avoid backpointer dereferencing in has_*_file()

2025-03-04T23:00:12+00:00

The PCI hotplug core contains five has_*_file() functions to determine
whether a certain sysfs file shall be added (or removed) for a given
hotplug slot.

The functions receive a struct pci_slot pointer which they have to
dereference back to a struct hotplug_slot.

Avoid by passing them a struct hotplug_slot pointer directly.

Link: https://lore.kernel.org/r/5b2f5b4ac45285953d00fd7637732a93fd40d26e.1740501868.git.lukas@wunner.de
Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Drop superfluous NULL pointer checks in has_*_file()

2025-03-04T23:00:12+00:00

The PCI hotplug core contains five has_*_file() functions to determine
whether a certain sysfs file shall be added (or removed) for a given
hotplug slot.

The functions perform NULL pointer checks for the hotplug_slot and its
hotplug_slot_ops.  However the callers already perform these checks:

  pci_hp_register()
    __pci_hp_register()
      __pci_hp_initialize()

  pci_hp_deregister()
    pci_hp_del()

The only way to actually trigger these checks is to call pci_hp_add()
without having called pci_hp_initialize().

Amend pci_hp_add() to catch that and drop the now superfluous NULL
pointer checks in has_*_file().

Drop the same superfluous checks from pci_hp_create_module_link(),
which is (only) called from pci_hp_add().

Link: https://lore.kernel.org/r/37d1928edf8c3201a8b10794f1db3142e16e02b9.1740501868.git.lukas@wunner.de
Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Drop superfluous try_module_get() calls

2025-03-04T23:00:12+00:00

In December 2002, historic commit

  https://git.kernel.org/tglx/history/c/bec7aa00ffe5
  ("[PATCH] more module warning fixes")

amended the PCI hotplug core to acquire a reference on the hotplug
driver module when a sysfs attribute is accessed.  That was necessary
because back in the day, sysfs code did not take any precautions to
prevent module unloading when an attribute was accessed.

Soon after in July 2003, historic commit

  https://git.kernel.org/tglx/history/c/1cf6d20f6078
  ("[PATCH] SYSFS: add module referencing to sysfs attribute files.")

addressed that deficiency.  But the commit neglected to remove the now
unnecessary reference acquisition from the PCI hotplug core.

The commit acquired a module reference for the entire duration between
open() and close() of a sysfs attribute.  This made it impossible to
unload a module while attributes were kept open by user space.
That's possible today:

When a hotplug driver module is unloaded, it removes sysfs attributes of
all its hotplug slots by calling pci_hp_del().  This will wait for any
concurrent user space operation to finish:

  pci_hp_del()
    fs_remove_slot()
      sysfs_remove_file()
        sysfs_remove_file_ns()
          kernfs_remove_by_name_ns()
            __kernfs_remove()
              kernfs_drain()

A user space operation such as read() briefly acquires a reference on
the attribute with kernfs_get_active().  kernfs_drain() waits until all
such references are released before allowing attribute removal.  Once
the attribute is removed, any subsequent user space operation on a still
open attribute file will return -ENODEV.

Thus, reference acquisition by the PCI hotplug core is still unnecessary
today.  So drop it at long last.

Link: https://lore.kernel.org/r/ed950fa2722967be4491146c7b867c1e7be11d37.1740501868.git.lukas@wunner.de
Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Drop superfluous pci_hotplug_slot_list

2025-03-04T23:00:12+00:00

The PCI hotplug core keeps a list of all registered slots.  Its sole
purpose is to WARN() on slot removal if another slot is using the same
name.

But this can never happen because already on slot creation, an error is
returned and multiple messages are emitted if a slot's name is
duplicated:

  pci_hp_register()
    __pci_hp_register()
      __pci_hp_initialize()
        pci_create_slot()
          kobject_init_and_add()
            kobject_add_varg()
              kobject_add_internal()
                create_dir()
                  sysfs_create_dir_ns()
                    kernfs_create_dir_ns()
                      sysfs_warn_dup()
                        pr_warn("cannot create duplicate filename ...")
                pr_err("%s failed for %s with -EEXIST, ...");

Drop the superfluous list.

Link: https://lore.kernel.org/r/603735bc50eb370bc7f1c358441ac671360bab25.1740501868.git.lukas@wunner.de
Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Remove "Returns" kerneldoc from void functions

2024-09-30T17:02:53+00:00

pci_hp_deregister() was converted to void by the commit 51bbf9bee34f ("PCI:
hotplug: Demidlayer registration with the core") but its kerneldoc still
describes the return value. pci_hp_del() and pci_hp_destroy() have been
void since they were introduced in that same commit.

Remove the return value description from the kerneldoc of those functions.

Link: https://lore.kernel.org/r/20240930124436.17908-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen 
Signed-off-by: Bjorn Helgaas

PCI: hotplug: Reorganize kerneldoc parameter names

2024-09-30T16:42:17+00:00

Reorganize kerneldoc parameter names to match the parameter order in the
function header.

Problems identified using Coccinelle.

Link: https://lore.kernel.org/r/20240930112121.95324-23-Julia.Lawall@inria.fr
Signed-off-by: Julia Lawall 
Signed-off-by: Bjorn Helgaas

PCI/sysfs: Use sysfs_emit() and sysfs_emit_at() in "show" functions

2021-06-04T03:14:47+00:00

The sysfs_emit() and sysfs_emit_at() functions were introduced to make
it less ambiguous which function is preferred when writing to the output
buffer in a device attribute's "show" callback [1].

Convert the PCI sysfs object "show" functions from sprintf(), snprintf()
and scnprintf() to sysfs_emit() and sysfs_emit_at() accordingly, as the
latter is aware of the PAGE_SIZE buffer and correctly returns the number
of bytes written into the buffer.

No functional change intended.

[1] Documentation/filesystems/sysfs.rst

Related commit: ad025f8e46f3 ("PCI/sysfs: Use sysfs_emit() and
sysfs_emit_at() in "show" functions").

Link: https://lore.kernel.org/r/20210603000112.703037-2-kw@linux.com
Signed-off-by: Krzysztof Wilczyński 
Signed-off-by: Bjorn Helgaas 
Reviewed-by: Logan Gunthorpe

PCI: hotplug: Drop hotplug_slot_info

2018-09-18T22:52:15+00:00

Ever since the PCI hotplug core was introduced in 2002, drivers had to
allocate and register a struct hotplug_slot_info for every slot:
https://git.kernel.org/tglx/history/c/a8a2069f432c

Apparently the idea was that drivers furnish the hotplug core with an
up-to-date card presence status, power status, latch status and
attention indicator status as well as notify the hotplug core of changes
thereof.  However only 4 out of 12 hotplug drivers bother to notify the
hotplug core with pci_hp_change_slot_info() and the hotplug core never
made any use of the information:  There is just a single macro in
pci_hotplug_core.c, GET_STATUS(), which uses the hotplug_slot_info if
the driver lacks the corresponding callback in hotplug_slot_ops.  The
macro is called when the user reads the attribute via sysfs.

Now, if the callback isn't defined, the attribute isn't exposed in sysfs
in the first place (see e.g. has_power_file()).  There are only two
situations when the hotplug_slot_info would actually be accessed:

* If the driver defines ->enable_slot or ->disable_slot but not
  ->get_power_status.

* If the driver defines ->set_attention_status but not
  ->get_attention_status.

There is no driver doing the former and just a single driver doing the
latter, namely pnv_php.c.  Amend it with a ->get_attention_status
callback.  With that, the hotplug_slot_info becomes completely unused by
the PCI hotplug core.  But a few drivers use it internally as a cache:

cpcihp uses it to cache the latch_status and adapter_status.
cpqhp uses it to cache the adapter_status.
pnv_php and rpaphp use it to cache the attention_status.
shpchp uses it to cache all four values.

Amend these drivers to cache the information in their private slot
struct.  shpchp's slot struct already contains members to cache the
power_status and adapter_status, so additional members are only needed
for the other two values.  In the case of cpqphp, the cached value is
only accessed in a single place, so instead of caching it, read the
current value from the hardware.

Caution:  acpiphp, cpci, cpqhp, shpchp, asus-wmi and eeepc-laptop
populate the hotplug_slot_info with initial values on probe.  That code
is herewith removed.  There is a theoretical chance that the code has
side effects without which the driver fails to function, e.g. if the
ACPI method to read the adapter status needs to be executed at least
once on probe.  That seems unlikely to me, still maintainers should
review the changes carefully for this possibility.

Rafael adds: "I'm not aware of any case in which it will break anything,
[...] but if that happens, it may be necessary to add the execution of
the control methods in question directly to the initialization part."

Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas 
Reviewed-by: Rafael J. Wysocki 
Acked-by: Tyrel Datwyler   # drivers/pci/hotplug/rpa*
Acked-by: Sebastian Ott         # drivers/pci/hotplug/s390*
Acked-by: Andy Shevchenko  # drivers/platform/x86
Cc: Len Brown 
Cc: Scott Murray 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: Oliver OHalloran 
Cc: Gavin Shan 
Cc: Gerald Schaefer 
Cc: Corentin Chary 
Cc: Darren Hart

PCI: hotplug: Constify hotplug_slot_ops

2018-09-18T22:52:15+00:00

Hotplug drivers cannot declare their hotplug_slot_ops const, making them
attractive targets for attackers, because upon registration of a hotplug
slot, __pci_hp_initialize() writes to the "owner" and "mod_name" members
in that struct.

Fix by moving these members to struct hotplug_slot and constify every
driver's hotplug_slot_ops except for pciehp.

pciehp constructs its hotplug_slot_ops at runtime based on the PCIe
port's capabilities, hence cannot declare them const.  It can be
converted to __write_rarely once that's mainlined:
http://www.openwall.com/lists/kernel-hardening/2016/11/16/3

Signed-off-by: Lukas Wunner 
Signed-off-by: Bjorn Helgaas 
Reviewed-by: Rafael J. Wysocki 
Acked-by: Tyrel Datwyler   # drivers/pci/hotplug/rpa*
Acked-by: Andy Shevchenko  # drivers/platform/x86
Cc: Len Brown 
Cc: Scott Murray 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: Oliver OHalloran 
Cc: Gavin Shan 
Cc: Sebastian Ott 
Cc: Gerald Schaefer 
Cc: Corentin Chary 
Cc: Darren Hart