ACPI / hotplug / PCI: Remove entries from bus->devices in reverse order

According to the changelog of commit 29ed1f29b68a (PCI: pciehp: Fix null
pointer deref when hot-removing SR-IOV device) it is unsafe to walk the
bus->devices list of a PCI bus and remove devices from it in direct order,
because that may lead to NULL pointer dereferences related to virtual
functions.

For this reason, change all of the bus->devices list walks in
acpiphp_glue.c during which devices may be removed to be carried out in
reverse order.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Move PCI rescan-remove locking to hotplug_event()

Commit 9217a984671e (ACPI / hotplug / PCI: Use global PCI rescan-remove
locking) modified ACPIPHP to protect its PCI device removal and addition
code paths from races against sysfs-driven rescan and remove operations
with the help of PCI rescan-remove locking.  However, it overlooked the
fact that hotplug_event_work() is not the only caller of hotplug_event()
which may also be called by dock_hotplug_event() and that code path
is missing the PCI rescan-remove locking.  This means that, although
the PCI rescan-remove lock is held as appropriate during the handling
of events originating from handle_hotplug_event(), the ACPIPHP's
operations resulting from dock events may still suffer the race
conditions that commit 9217a984671e was supposed to eliminate.

To address that problem, move the PCI rescan-remove locking from
hotplug_event_work() to hotplug_event() so that it is used regardless
of the way that function is invoked.

Revamps: 9217a984671e (ACPI / hotplug / PCI: Use global PCI rescan-remove locking)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Simplify disable_slot()

After recent PCI core changes related to the rescan/remove locking,
the ACPIPHP's disable_slot() function is only called under the
general PCI rescan/remove lock, so it doesn't have to use
dev_in_slot() any more to avoid race conditions.  Make it simply
walk the devices on the bus and drop the ones in the slot being
disabled and drop dev_in_slot() which has no more users.

Moreover, to avoid problems described in the changelog of commit
29ed1f29b68a (PCI: pciehp: Fix null pointer deref when hot-removing
SR-IOV device), make disable_slot() carry out the list walk in
reverse order.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Proper kerneldoc comments for enumeration/removal

Add proper kerneldoc comments describing acpiphp_enumerate_slots()
and acpiphp_remove_slots().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Simplify register_slot()

The err label in register_slot() is only jumped to from one place,
so move the code under the label to that place and drop the label.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Drop acpiphp_bus_trim()

If trim_stale_devices() calls acpi_bus_trim() directly, we can
save a potentially costly acpi_bus_get_device() invocation.  After
making that change acpiphp_bus_trim() would only be called from one
place, so move the code from it to that place and drop it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Rework acpiphp_no_hotplug()

If a struct acpi_device pointer is passed to acpiphp_no_hotplug()
instead of an ACPI handle, the function won't need to call
acpi_bus_get_device(), which may be costly, any more.  Then,
trim_stale_devices() can call acpiphp_no_hotplug() passing
the struct acpi_device object it already has directly to that
function.

Make those changes and update slot_no_hotplug() accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Store acpi_device pointer in acpiphp_context

After recent modifications of the ACPI core making it create a struct
acpi_device object for every namespace node representing a device
regardless of the current status of that device the ACPIPHP code
can store a struct acpi_device pointer instead of an ACPI handle
in struct acpiphp_context.  This immediately makes it possible to
avoid making potentially costly calls to acpi_bus_get_device() in
two places and allows some more simplifications to be made going
forward.

The reason why that is correct is because ACPIPHP only installs
hotify handlers for namespace nodes that exist when
acpiphp_enumerate_slots() is called for their parent bridge.
That only happens if the parent bridge has an ACPI companion
associated with it, which means that the ACPI namespace scope
in question has been scanned already at that point.  That, in
turn, means that struct acpi_device objects have been created
for all namespace nodes in that scope and pointers to those
objects can be stored directly instead of their ACPI handles.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Drop acpiphp_bus_add()

acpiphp_bus_add() is only called from one place, so move the code out
of it into that place and drop it.  Also make that code use
func_to_acpi_device() to get the struct acpi_device pointer it needs
instead of calling acpi_bus_get_device() which may be costly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Drop crit_sect locking

After recent PCI core changes related to the rescan/remove locking,
the code sections under crit_sect mutexes from ACPIPHP slot objects
are always executed under the general PCI rescan/remove lock.
For this reason, the crit_sect mutexes are simply redundant, so drop
them.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Simplify hotplug_event()

A few lines of code can be cut from hotplug_event() by defining
and initializing the slot variable at the top of the function,
so do that.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Use acpi_handle_debug() in hotplug_event()

Make hotplug_event() use acpi_handle_debug() instead of an open-coded
debug message printing and clean up the messages printed by it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug: Do not pass ACPI handles to ACPI dock operations

None of the existing users of struct acpi_dock_ops actually needs the
first argument of its member functions, so redefine those functions
to take only two arguments, the event type and data pointer, and
update the users of struct acpi_dock_ops accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug: Fix theoretical race in acpi_hotplug_notify_cb()

There is a slight possibility for the ACPI device object pointed to
by adev in acpi_hotplug_notify_cb() to become invalid between the
acpi_bus_get_device() that it comes from and the subsequent get_device().
Namely, if acpi_scan_drop_device() runs concurrently with respect to
acpi_hotplug_notify_cb() and acpi_device_del_list is not empty,
acpi_device_del_work_fn() may delete the device object in question
without waiting for the ACPI events workqueue to drain, which very
well may happen right after a successful execution of
acpi_bus_get_device() in acpi_hotplug_notify_cb().

To prevent that from happening, run acpi_bus_get_device() and the
subsequent get_device() in acpi_hotplug_notify_cb() under
acpi_device_del_lock, so that the deletion of the given device
object cannot be queued up by acpi_scan_drop_device() between the
two.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Move hotplug context locking to core

Subsequent changes will require the ACPI core to acquire the lock
protecting the ACPIPHP hotplug contexts, so move the definition of
the lock to the core and change its name to be more generic.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Consolidate ACPIPHP with ACPI core hotplug

The ACPI-based PCI hotplug (ACPIPHP) code currently attaches its
hotplug context objects directly to ACPI namespace nodes representing
hotplug devices.  However, after recent changes causing struct
acpi_device to be created for every namespace node representing a
device (regardless of its status), that is not necessary any more.
Moreover, it's vulnerable to a theoretical issue that the ACPI
handle passed in the context between handle_hotplug_event() and
hotplug_event_work() may become invalid in the meantime (as a
result of a concurrent table unload).

In principle, this issue might be addressed by adding a non-empty
release handler for ACPIPHP hotplug context objects analogous to
acpi_scan_drop_device(), but that would duplicate the code in that
function and in acpi_device_del_work_fn().  For this reason, it's
better to modify ACPIPHP to attach its device hotplug contexts to
struct device objects representing hotplug devices and make it
use acpi_hotplug_notify_cb() as its notify handler.  At the same
time, acpi_device_hotplug() can be modified to dispatch the new
.hp.event() callback pointing to acpiphp_hotplug_event() from ACPI
device objects associated with PCI devices and use the generic
ACPI device hotplug code for device objects with scan handlers
attached to them.

This allows the existing code duplication between ACPIPHP and the
ACPI core to be reduced too and makes further ACPI-based device
hotplug consolidation possible.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Rework the handling of eject requests

To avoid the need to install a hotplug notify handler for each ACPI
namespace node representing a device and having a matching scan
handler, move the check whether or not the ejection of the given
device is enabled through its scan handler from acpi_hotplug_notify_cb()
to acpi_generic_hotplug_event().  Also, move the execution of
ACPI_OST_SC_EJECT_IN_PROGRESS _OST to acpi_generic_hotplug_event(),
because in acpi_hotplug_notify_cb() or in acpi_eject_store() we really
don't know whether or not the eject is going to be in progress (for
example, acpi_hotplug_execute() may still fail without queuing up the
work item).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Simplify acpi_install_hotplug_notify_handler()

Since acpi_hotplug_notify_cb() does not use its data argument any
more, the second argument of acpi_install_hotplug_notify_handler()
can be dropped, so do that and update its callers accordingly.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
ACPI / hotplug / PCI: Hotplug notifications from acpi_bus_notify()

Since acpi_bus_notify() is executed on all notifications for all
devices anyway, rename acpi_hotplug_notify_cb() to acpi_system_notify()
and call it directly from acpi_bus_notify() instead of installing
notify handlers pointing to it for all hotplug devices.

This change reduces both the size and complexity of ACPI-based device
hotplug code.  Moreover, since acpi_system_notify() only does
significant things for devices that either have an ACPI scan handler,
or have a hotplug context with .eject() defined, and those devices
had notify handlers pointing to acpi_hotplug_notify_cb() installed
before anyway, this modification shouldn't change functionality.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
PM / QoS: Rename device resume latency QoS items

Rename symbols, variables, functions and structure fields related do
the resume latency device PM QoS type so that it is clear where they
belong (in particular, to avoid confusion with the latency tolerance
device PM QoS type introduced by a subsequent changeset).

Update the PM QoS documentation to better reflect its current state.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>