kernel/linux.git/drivers/pci/hotplug/pci_hotplug_core.c, branch v6.19.12

PCI: hotplug: Drop superfluous #include directives

2025-04-17T19:36:29+00:00

In February 2003, historic commit https://git.kernel.org/tglx/history/c/280c1c9a0ea4 ("[PATCH] PCI Hotplug: Replace pcihpfs with sysfs.") removed all invocations of __get_free_page() and free_page() from the PCI hotplug core without also removing the #include directive. It removed all invocations of kern_mount(), mntget() and mntput() without also removing the #include directive. It removed all invocations of lookup_hash() without also removing the #include directive. It removed all invocations of copy_to_user() and copy_from_user() without also removing the #include directive. These #include directives are still unnecessary today, so drop them. Signed-off-by: Lukas Wunner Signed-off-by: Bjorn Helgaas Link: https://patch.msgid.link/c19e25bf2cefecc14e0822c6a9bb3a7f546258bc.1744640331.git.lukas@wunner.de

PCI: pciehp: Ignore Link Down/Up caused by Secondary Bus Reset

2025-04-15T21:03:44+00:00

When a Secondary Bus Reset is issued at a hotplug port, it causes a Data Link Layer State Changed event as a side effect. On hotplug ports using in-band presence detect, it additionally causes a Presence Detect Changed event. These spurious events should not result in teardown and re-enumeration of the device in the slot. Hence commit 2e35afaefe64 ("PCI: pciehp: Add reset_slot() method") masked the Presence Detect Changed Enable bit in the Slot Control register during a Secondary Bus Reset. Commit 06a8d89af551 ("PCI: pciehp: Disable link notification across slot reset") additionally masked the Data Link Layer State Changed Enable bit. However masking those bits only disables interrupt generation (PCIe r6.2 sec 6.7.3.1). The events are still visible in the Slot Status register and picked up by the IRQ handler if it runs during a Secondary Bus Reset. This can happen if the interrupt is shared or if an unmasked hotplug event occurs, e.g. Attention Button Pressed or Power Fault Detected. The likelihood of this happening used to be small, so it wasn't much of a problem in practice. That has changed with the recent introduction of bandwidth control in v6.13-rc1 with commit 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller"): Bandwidth control shares the interrupt with PCIe hotplug. A Secondary Bus Reset causes a Link Bandwidth Notification, so the hotplug IRQ handler runs, picks up the masked events and tears down the device in the slot. As a result, Joel reports VFIO passthrough failure of a GPU, which Ilpo root-caused to the incorrect handling of masked hotplug events. Clearly, a more reliable way is needed to ignore spurious hotplug events. For Downstream Port Containment, a new ignore mechanism was introduced by commit a97396c6eb13 ("PCI: pciehp: Ignore Link Down/Up caused by DPC"). It has been working reliably for the past four years. Adapt it for Secondary Bus Resets. Introduce two helpers to annotate code sections which cause spurious link changes: pci_hp_ignore_link_change() and pci_hp_unignore_link_change() Use those helpers in lieu of masking interrupts in the Slot Control register. Introduce a helper to check whether such a code section is executing concurrently and if so, await it: pci_hp_spurious_link_change() Invoke the helper in the hotplug IRQ thread pciehp_ist(). Re-use the IRQ thread's existing code which ignores DPC-induced link changes unless the link is unexpectedly down after reset recovery or the device was replaced during the bus reset. That code block in pciehp_ist() was previously only executed if a Data Link Layer State Changed event has occurred. Additionally execute it for Presence Detect Changed events. That's necessary for compatibility with PCIe r1.0 hotplug ports because Data Link Layer State Changed didn't exist before PCIe r1.1. DPC was added with PCIe r3.1 and thus DPC-capable hotplug ports always support Data Link Layer State Changed events. But the same cannot be assumed for Secondary Bus Reset, which already existed in PCIe r1.0. Secondary Bus Reset is only one of many causes of spurious link changes. Others include runtime suspend to D3cold, firmware updates or FPGA reconfiguration. The new pci_hp_{,un}ignore_link_change() helpers may be used by all kinds of drivers to annotate such code sections, hence their declarations are publicly visible in . A case in point is the Mellanox Ethernet driver which disables a firmware reset feature if the Ethernet card is attached to a hotplug port, see commit 3d7a3f2612d7 ("net/mlx5: Nack sync reset request when HotPlug is enabled"). Going forward, PCIe hotplug will be able to cope gracefully with all such use cases once the code sections are properly annotated. The new helpers internally use two bits in struct pci_dev's priv_flags as well as a wait_queue. This mirrors what was done for DPC by commit a97396c6eb13 ("PCI: pciehp: Ignore Link Down/Up caused by DPC"). That may be insufficient if spurious link changes are caused by multiple sources simultaneously. An example might be a Secondary Bus Reset issued by AER during FPGA reconfiguration. If this turns out to happen in real life, support for it can easily be added by replacing the PCI_LINK_CHANGING flag with an atomic_t counter incremented by pci_hp_ignore_link_change() and decremented by pci_hp_unignore_link_change(). Instead of awaiting a zero PCI_LINK_CHANGING flag, the pci_hp_spurious_link_change() helper would then simply await a zero counter. Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller") Reported-by: Joel Mathew Thomas Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219765 Signed-off-by: Lukas Wunner Signed-off-by: Bjorn Helgaas Tested-by: Joel Mathew Thomas Reviewed-by: Kuppuswamy Sathyanarayanan Reviewed-by: Ilpo Järvinen Link: https://patch.msgid.link/d04deaf49d634a2edf42bf3c06ed81b4ca54d17b.1744298239.git.lukas@wunner.de

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