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, 23 insertions, 0 deletions

diff --git a/Documentation/crypto/api-akcipher.rst b/Documentation/crypto/api-akcipher.rst
new file mode 100644
index 000000000..a31f5aef7
--- /dev/null
+++ b/Documentation/crypto/api-akcipher.rst
@@ -0,0 +1,23 @@
+Asymmetric Cipher
+=================
+
+Asymmetric Cipher Algorithm Definitions
+---------------------------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: akcipher_alg akcipher_request
+
+Asymmetric Cipher API
+---------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :doc: Generic Public Key Cipher API
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: crypto_alloc_akcipher crypto_free_akcipher crypto_akcipher_set_pub_key crypto_akcipher_set_priv_key crypto_akcipher_maxsize crypto_akcipher_encrypt crypto_akcipher_decrypt
+
+Asymmetric Cipher Request Handle
+--------------------------------
+
+.. kernel-doc:: include/crypto/akcipher.h
+   :functions: akcipher_request_alloc akcipher_request_free akcipher_request_set_callback akcipher_request_set_crypt