PCI hotplug: acpiphp: Prevent deadlock on PCI-to-PCI bridge remove

I originally submitted a patch to workaround this by pushing all Ejection
Requests and Device Checks onto the kacpi_hotplug queue.

http://marc.info/?l=linux-acpi&m=131678270930105&w=2

The patch is still insufficient in that Bus Checks also need to be added.

Rather than add all events, including non-PCI-hotplug events, to the
hotplug queue, mjg suggested that a better approach would be to modify
the acpiphp driver so only acpiphp events would be added to the
kacpi_hotplug queue.

It's a longer patch, but at least we maintain the benefit of having separate
queues in ACPI.  This, of course, is still only a workaround the problem.
As Bjorn and mjg pointed out, we have to refactor a lot of this code to do
the right thing but at this point it is a better to have this code working.

The acpi core places all events on the kacpi_notify queue.  When the acpiphp
driver is loaded and a PCI card with a PCI-to-PCI bridge is removed the
following call sequence occurs:

cleanup_p2p_bridge()
	    -> cleanup_bridge()
		    -> acpi_remove_notify_handler()
			    -> acpi_os_wait_events_complete()
				    -> flush_workqueue(kacpi_notify_wq)

which is the queue we are currently executing on and the process will hang.

Move all hotplug acpiphp events onto the kacpi_hotplug workqueue.  In
handle_hotplug_event_bridge() and handle_hotplug_event_func() we can simply
push the rest of the work onto the kacpi_hotplug queue and then avoid the
deadlock.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: mjg@redhat.com
Cc: bhelgaas@google.com
Cc: linux-acpi@vger.kernel.org
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 94 insertions, 15 deletions

diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
index 220285760b68..596172b4ae95 100644
--- a/drivers/pci/hotplug/acpiphp_glue.c
+++ b/drivers/pci/hotplug/acpiphp_glue.c
@@ -48,6 +48,7 @@
 #include <linux/pci-acpi.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/acpi.h>
 
 #include "../pci.h"
 #include "acpiphp.h"
@@ -1149,15 +1150,35 @@ check_sub_bridges(acpi_handle handle, u32 lvl, void *context, void **rv)
         return AE_OK ;
 }
 
-/**
- * handle_hotplug_event_bridge - handle ACPI event on bridges
- * @handle: Notify()'ed acpi_handle
- * @type: Notify code
- * @context: pointer to acpiphp_bridge structure
- *
- * Handles ACPI event notification on {host,p2p} bridges.
- */
-static void handle_hotplug_event_bridge(acpi_handle handle, u32 type, void *context)
+struct acpiphp_hp_work {
+        struct work_struct work;
+        acpi_handle handle;
+        u32 type;
+        void *context;
+};
+
+static void alloc_acpiphp_hp_work(acpi_handle handle, u32 type,
+                                  void *context,
+                                  void (*func)(struct work_struct *work))
+{
+        struct acpiphp_hp_work *hp_work;
+        int ret;
+
+        hp_work = kmalloc(sizeof(*hp_work), GFP_KERNEL);
+        if (!hp_work)
+                return;
+
+        hp_work->handle = handle;
+        hp_work->type = type;
+        hp_work->context = context;
+
+        INIT_WORK(&hp_work->work, func);
+        ret = queue_work(kacpi_hotplug_wq, &hp_work->work);
+        if (!ret)
+                kfree(hp_work);
+}
+
+static void _handle_hotplug_event_bridge(struct work_struct *work)
 {
         struct acpiphp_bridge *bridge;
         char objname[64];
@@ -1165,11 +1186,18 @@ static void handle_hotplug_event_bridge(acpi_handle handle, u32 type, void *cont
                                       .pointer = objname };
         struct acpi_device *device;
         int num_sub_bridges = 0;
+        struct acpiphp_hp_work *hp_work;
+        acpi_handle handle;
+        u32 type;
+
+        hp_work = container_of(work, struct acpiphp_hp_work, work);
+        handle = hp_work->handle;
+        type = hp_work->type;
 
         if (acpi_bus_get_device(handle, &device)) {
                 /* This bridge must have just been physically inserted */
                 handle_bridge_insertion(handle, type);
-                return;
+                goto out;
         }
 
         bridge = acpiphp_handle_to_bridge(handle);
@@ -1180,7 +1208,7 @@ static void handle_hotplug_event_bridge(acpi_handle handle, u32 type, void *cont
 
         if (!bridge && !num_sub_bridges) {
                 err("cannot get bridge info\n");
-                return;
+                goto out;
         }
 
         acpi_get_name(handle, ACPI_FULL_PATHNAME, &buffer);
@@ -1241,22 +1269,49 @@ static void handle_hotplug_event_bridge(acpi_handle handle, u32 type, void *cont
                 warn("notify_handler: unknown event type 0x%x for %s\n", type, objname);
                 break;
         }
+
+out:
+        kfree(hp_work); /* allocated in handle_hotplug_event_bridge */
 }
 
 /**
- * handle_hotplug_event_func - handle ACPI event on functions (i.e. slots)
+ * handle_hotplug_event_bridge - handle ACPI event on bridges
  * @handle: Notify()'ed acpi_handle
  * @type: Notify code
- * @context: pointer to acpiphp_func structure
+ * @context: pointer to acpiphp_bridge structure
  *
- * Handles ACPI event notification on slots.
+ * Handles ACPI event notification on {host,p2p} bridges.
  */
-static void handle_hotplug_event_func(acpi_handle handle, u32 type, void *context)
+static void handle_hotplug_event_bridge(acpi_handle handle, u32 type,
+                                        void *context)
+{
+        /*
+         * Currently the code adds all hotplug events to the kacpid_wq
+         * queue when it should add hotplug events to the kacpi_hotplug_wq.
+         * The proper way to fix this is to reorganize the code so that
+         * drivers (dock, etc.) do not call acpi_os_execute(), etc.
+         * For now just re-add this work to the kacpi_hotplug_wq so we
+         * don't deadlock on hotplug actions.
+         */
+        alloc_acpiphp_hp_work(handle, type, context,
+                              _handle_hotplug_event_bridge);
+}
+
+static void _handle_hotplug_event_func(struct work_struct *work)
 {
         struct acpiphp_func *func;
         char objname[64];
         struct acpi_buffer buffer = { .length = sizeof(objname),
                                       .pointer = objname };
+        struct acpiphp_hp_work *hp_work;
+        acpi_handle handle;
+        u32 type;
+        void *context;
+
+        hp_work = container_of(work, struct acpiphp_hp_work, work);
+        handle = hp_work->handle;
+        type = hp_work->type;
+        context = hp_work->context;
 
         acpi_get_name(handle, ACPI_FULL_PATHNAME, &buffer);
 
@@ -1291,8 +1346,32 @@ static void handle_hotplug_event_func(acpi_handle handle, u32 type, void *contex
                 warn("notify_handler: unknown event type 0x%x for %s\n", type, objname);
                 break;
         }
+
+        kfree(hp_work); /* allocated in handle_hotplug_event_func */
 }
 
+/**
+ * handle_hotplug_event_func - handle ACPI event on functions (i.e. slots)
+ * @handle: Notify()'ed acpi_handle
+ * @type: Notify code
+ * @context: pointer to acpiphp_func structure
+ *
+ * Handles ACPI event notification on slots.
+ */
+static void handle_hotplug_event_func(acpi_handle handle, u32 type,
+                                      void *context)
+{
+        /*
+         * Currently the code adds all hotplug events to the kacpid_wq
+         * queue when it should add hotplug events to the kacpi_hotplug_wq.
+         * The proper way to fix this is to reorganize the code so that
+         * drivers (dock, etc.) do not call acpi_os_execute(), etc.
+         * For now just re-add this work to the kacpi_hotplug_wq so we
+         * don't deadlock on hotplug actions.
+         */
+        alloc_acpiphp_hp_work(handle, type, context,
+                              _handle_hotplug_event_func);
+}
 
 static acpi_status
 find_root_bridges(acpi_handle handle, u32 lvl, void *context, void **rv)