thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 84 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/access-controllers/access-controllers.yaml b/Documentation/devicetree/bindings/access-controllers/access-controllers.yaml
new file mode 100644
index 000000000..99e2865f0
--- /dev/null
+++ b/Documentation/devicetree/bindings/access-controllers/access-controllers.yaml
@@ -0,0 +1,84 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/access-controllers/access-controllers.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic Domain Access Controllers
+
+maintainers:
+  - Oleksii Moisieiev <oleksii_moisieiev@epam.com>
+
+description: |+
+  Common access controllers properties
+
+  Access controllers are in charge of stating which of the hardware blocks under
+  their responsibility (their domain) can be accesssed by which compartment. A
+  compartment can be a cluster of CPUs (or coprocessors), a range of addresses
+  or a group of hardware blocks. An access controller's domain is the set of
+  resources covered by the access controller.
+
+  This device tree binding can be used to bind devices to their access
+  controller provided by access-controllers property. In this case, the device
+  is a consumer and the access controller is the provider.
+
+  An access controller can be represented by any node in the device tree and
+  can provide one or more configuration parameters, needed to control parameters
+  of the consumer device. A consumer node can refer to the provider by phandle
+  and a set of phandle arguments, specified by '#access-controller-cells'
+  property in the access controller node.
+
+  Access controllers are typically used to set/read the permissions of a
+  hardware block and grant access to it. Any of which depends on the access
+  controller. The capabilities of each access controller are defined by the
+  binding of the access controller device.
+
+  Each node can be a consumer for the several access controllers.
+
+# always select the core schema
+select: true
+
+properties:
+  "#access-controller-cells":
+    description:
+      Number of cells in an access-controllers specifier;
+      Can be any value as specified by device tree binding documentation
+      of a particular provider. The node is an access controller.
+
+  access-controller-names:
+    $ref: /schemas/types.yaml#/definitions/string-array
+    description:
+      A list of access-controllers names, sorted in the same order as
+      access-controllers entries. Consumer drivers will use
+      access-controller-names to match with existing access-controllers entries.
+
+  access-controllers:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description:
+      A list of access controller specifiers, as defined by the
+      bindings of the access-controllers provider.
+
+additionalProperties: true
+
+examples:
+  - |
+    clock_controller: access-controllers@50000 {
+        reg = <0x50000 0x400>;
+        #access-controller-cells = <2>;
+    };
+
+    bus_controller: bus@60000 {
+        reg = <0x60000 0x10000>;
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges;
+        #access-controller-cells = <3>;
+
+        uart4: serial@60100 {
+            reg = <0x60100 0x400>;
+            clocks = <&clk_serial>;
+            access-controllers = <&clock_controller 1 2>,
+                                 <&bus_controller 1 3 5>;
+            access-controller-names = "clock", "bus";
+        };
+    };