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, 19 insertions, 0 deletions

diff --git a/Documentation/accel/rocket/index.rst b/Documentation/accel/rocket/index.rst
new file mode 100644
index 000000000..70f97bccf
--- /dev/null
+++ b/Documentation/accel/rocket/index.rst
@@ -0,0 +1,19 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=====================================
+ accel/rocket Rockchip NPU driver
+=====================================
+
+The accel/rocket driver supports the Neural Processing Units (NPUs) inside some
+Rockchip SoCs such as the RK3588. Rockchip calls it RKNN and sometimes RKNPU.
+
+The hardware is described in chapter 36 in the RK3588 TRM.
+
+This driver just powers the hardware on and off, allocates and maps buffers to
+the device and submits jobs to the frontend unit. Everything else is done in
+userspace, as a Gallium driver (also called rocket) that is part of the Mesa3D
+project.
+
+Hardware currently supported:
+
+* RK3588