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, 120 insertions, 0 deletions

diff --git a/Documentation/sphinx-static/theme_overrides.css b/Documentation/sphinx-static/theme_overrides.css
new file mode 100644
index 000000000..79000b26e
--- /dev/null
+++ b/Documentation/sphinx-static/theme_overrides.css
@@ -0,0 +1,120 @@
+/* -*- coding: utf-8; mode: css -*-
+ *
+ * Sphinx HTML theme customization: read the doc
+ * Please don't add any color definition here, as the theme should
+ * work for both normal and dark modes.
+ */
+
+/* Improve contrast and increase size for easier reading. */
+
+body {
+	font-family: serif;
+	font-size: 100%;
+}
+
+h1, h2, .rst-content .toctree-wrapper p.caption, h3, h4, h5, h6, legend {
+	font-family: sans-serif;
+}
+
+div[class^="highlight"] pre {
+	font-family: monospace;
+	font-size: 100%;
+}
+
+.wy-menu-vertical {
+	font-family: sans-serif;
+}
+
+.c {
+	font-style: normal;
+}
+
+p {
+	font-size: 100%;
+}
+
+/* Interim: Code-blocks with line nos - lines and line numbers don't line up.
+ * see: https://github.com/rtfd/sphinx_rtd_theme/issues/419
+ */
+
+div[class^="highlight"] pre {
+    line-height: normal;
+}
+.rst-content .highlight > pre {
+    line-height: normal;
+}
+
+/* Keep fields from being strangely far apart due to inheirited table CSS. */
+.rst-content table.field-list th.field-name {
+    padding-top: 1px;
+    padding-bottom: 1px;
+}
+.rst-content table.field-list td.field-body {
+    padding-top: 1px;
+    padding-bottom: 1px;
+}
+
+@media screen {
+
+    /* content column
+     *
+     * RTD theme's default is 800px as max width for the content, but we have
+     * tables with tons of columns, which need the full width of the view-port.
+     */
+
+    .wy-nav-content{max-width: none; }
+
+    /* table:
+     *
+     *   - Sequences of whitespace should collapse into a single whitespace.
+     *   - make the overflow auto (scrollbar if needed)
+     *   - align caption "left" ("center" is unsuitable on vast tables)
+     */
+
+    .wy-table-responsive table td { white-space: normal; }
+    .wy-table-responsive { overflow: auto; }
+    .rst-content table.docutils caption { text-align: left; font-size: 100%; }
+
+    /* captions:
+     *
+     *   - captions should have 100% (not 85%) font size
+     *   - hide the permalink symbol as long as link is not hovered
+     */
+
+    caption, .wy-table caption, .rst-content table.field-list caption {
+        font-size: 100%;
+    }
+    caption a.headerlink { opacity: 0; }
+    caption a.headerlink:hover { opacity: 1; }
+
+    /* Menu selection and keystrokes */
+
+    span.menuselection {
+	font-family: "Courier New", Courier, monospace
+    }
+
+    code.kbd, code.kbd span {
+	font-weight: bold;
+	font-family: "Courier New", Courier, monospace
+    }
+
+    /* fix bottom margin of lists items */
+
+    .rst-content .section ul li:last-child, .rst-content .section ul li p:last-child {
+          margin-bottom: 12px;
+    }
+
+    /* inline literal: drop the borderbox, padding and red color */
+
+    code, .rst-content tt, .rst-content code {
+        color: inherit;
+        border: none;
+        padding: unset;
+        background: inherit;
+        font-size: 85%;
+    }
+
+    .rst-content tt.literal,.rst-content tt.literal,.rst-content code.literal {
+        color: inherit;
+    }
+}