[PATCH 5/24][New] ACPI / hotplug / PCI: Fix bridge removal race vs dock events

From: Rafael J. Wysocki
Date: Mon Feb 03 2014 - 18:30:43 EST

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

If a PCI bridge with an ACPIPHP context attached is removed via
sysfs, the code path executed as a result is the following:

unregister_hotplug_dock_device (drops dock references to the bridge)
acpiphp_put_context (for each child, under context lock)
kfree (context)

Now, if a dock event affecting one of the bridge's child devices
occurs (roughly at the same time), it will lead to the following code

hotplug_event (dereferences context)

That may lead to a kernel crash in hotplug_event() if it is executed
after the last kfree() in the bridge removal code path.

To prevent that from happening, add a wrapper around hotplug_event()
called dock_event() and point the .handler pointer in acpiphp_dock_ops
to it. Make that wrapper retrieve the device's ACPIPHP context using
acpiphp_get_context() (instead of taking it from the data argument)
under acpiphp_context_lock and check if the parent bridge's
is_going_away flag is set. If that flag is set, it will return
immediately and if it is not set it will grab a reference to the
device's parent bridge before executing hotplug_event().

Then, in the above scenario, the reference to the parent bridge
held by dock_event() will prevent free_bridge() from being executed
for it until hotplug_event() returns.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
drivers/pci/hotplug/acpiphp_glue.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/pci/hotplug/acpiphp_glue.c
--- linux-pm.orig/drivers/pci/hotplug/acpiphp_glue.c
+++ linux-pm/drivers/pci/hotplug/acpiphp_glue.c
@@ -210,10 +210,29 @@ static void post_dock_fixups(acpi_handle

+static void dock_event(acpi_handle handle, u32 type, void *data)
+ struct acpiphp_context *context;
+ mutex_lock(&acpiphp_context_lock);
+ context = acpiphp_get_context(handle);
+ if (!context || WARN_ON(context->handle != handle)
+ || context->func.parent->is_going_away) {
+ mutex_unlock(&acpiphp_context_lock);
+ return;
+ }
+ get_bridge(context->func.parent);
+ acpiphp_put_context(context);
+ mutex_unlock(&acpiphp_context_lock);
+ hotplug_event(handle, type, data);
+ put_bridge(context->func.parent);

static const struct acpi_dock_ops acpiphp_dock_ops = {
.fixup = post_dock_fixups,
- .handler = hotplug_event,
+ .handler = dock_event,

/* Check whether the PCI device is managed by native PCIe hotplug driver */

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