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, 94 insertions, 0 deletions

diff --git a/Documentation/gpu/amdgpu/ptl.rst b/Documentation/gpu/amdgpu/ptl.rst
new file mode 100644
index 000000000..c7f16dea7
--- /dev/null
+++ b/Documentation/gpu/amdgpu/ptl.rst
@@ -0,0 +1,94 @@
+=======================================
+Peak Tops Limiter (PTL) sysfs Interface
+=======================================
+
+Overview
+--------
+The Peak Tops Limiter (PTL) sysfs interface enables users to control and
+configure the PTL feature for each GPU individually.  All PTL-related
+sysfs files are located under `/sys/class/drm/cardX/device/ptl/`, where
+`X` is the GPU index.  Through these files, users can enable or disable
+PTL, set preferred data formats, and query supported formats for each GPU.
+
+PTL sysfs files
+----------------
+The following files are available under `/sys/class/drm/cardX/device/ptl/`:
+
+- `ptl_enable`
+- `ptl_format`
+- `ptl_supported_formats`
+
+PTL Enable/Disable
+------------------
+File: `ptl_enable`
+Type: Read/Write (rw)
+
+Read: Returns the current PTL status as a string: `enabled` if PTL
+is active, or `disabled` if inactive.
+
+Write:
+
+- Write `1` or `enabled` to enable PTL
+- Write `0` or `disabled` to disable PTL
+
+Examples::
+
+    # Query PTL status
+    cat /sys/class/drm/card1/device/ptl/ptl_enable
+    # Output: enabled
+
+    # Enable PTL
+    sudo bash -c "echo 1 > /sys/class/drm/card1/device/ptl/ptl_enable"
+
+    # Disable PTL
+    sudo bash -c "echo 0 > /sys/class/drm/card1/device/ptl/ptl_enable"
+
+PTL Format (Preferred Data Formats)
+-----------------------------------
+File: `ptl_format`
+Type: Read/Write (rw)
+
+Read: Returns the two preferred formats, e.g. `I8,F32`.
+
+Write: Accepts two formats separated by a comma, e.g. `I8,F32`.
+
+- Both formats must be supported and different.
+- If an invalid format is provided (not supported, or both formats are the
+  same), the driver will return "write error: Invalid argument".
+
+Examples::
+
+    # Query PTL formats
+    cat /sys/class/drm/card1/device/ptl/ptl_format
+    # Output: I8,F32
+
+    # Set PTL formats
+    sudo bash -c "echo I8,F32 > /sys/class/drm/card1/device/ptl/ptl_format"
+
+Supported Formats
+-----------------
+File: `ptl_supported_formats`
+Type: Read-only (r)
+
+Read: Returns a comma-separated list of supported formats, e.g.
+`I8,F16,BF16,F32,F64`.
+
+Example::
+
+    # Check supported formats
+    cat /sys/class/drm/card1/device/ptl/ptl_supported_formats
+    # Output: I8,F16,BF16,F32,F64
+
+Behavioral Notes
+----------------
+- PTL formats can only be set when PTL is enabled.
+- If PTL is disabled, `ptl_format` returns `N/A`.
+- Only two formats can be set at a time, and they must be from the supported set and different..
+- All commands support per-GPU targeting.
+- Root permission is required to enable/disable PTL or change formats.
+- If the hardware does not support PTL, the PTL sysfs directory will not
+  be created.
+
+Implementation
+--------------
+The PTL sysfs nodes are implemented in `drivers/gpu/drm/amd/amdgpu/amdgpu_psp.c`.