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, 210 insertions, 0 deletions

diff --git a/Documentation/gpu/amdgpu/debugfs.rst b/Documentation/gpu/amdgpu/debugfs.rst
new file mode 100644
index 000000000..151d8bfc7
--- /dev/null
+++ b/Documentation/gpu/amdgpu/debugfs.rst
@@ -0,0 +1,210 @@
+==============
+AMDGPU DebugFS
+==============
+
+The amdgpu driver provides a number of debugfs files to aid in debugging
+issues in the driver.  These are usually found in
+/sys/kernel/debug/dri/<num>.
+
+DebugFS Files
+=============
+
+amdgpu_benchmark
+----------------
+
+Run benchmarks using the DMA engine the driver uses for GPU memory paging.
+Write a number to the file to run the test.  The results are written to the
+kernel log.  VRAM is on device memory (dGPUs) or carve out (APUs) and GTT
+(Graphics Translation Tables) is system memory that is accessible by the GPU.
+The following tests are available:
+
+- 1: simple test, VRAM to GTT and GTT to VRAM
+- 2: simple test, VRAM to VRAM
+- 3: GTT to VRAM, buffer size sweep, powers of 2
+- 4: VRAM to GTT, buffer size sweep, powers of 2
+- 5: VRAM to VRAM, buffer size sweep, powers of 2
+- 6: GTT to VRAM, buffer size sweep, common display sizes
+- 7: VRAM to GTT, buffer size sweep, common display sizes
+- 8: VRAM to VRAM, buffer size sweep, common display sizes
+
+amdgpu_test_ib
+--------------
+
+Read this file to run simple IB (Indirect Buffer) tests on all kernel managed
+rings.  IBs are command buffers usually generated by userspace applications
+which are submitted to the kernel for execution on an particular GPU engine.
+This just runs the simple IB tests included in the kernel.  These tests
+are engine specific and verify that IB submission works.
+
+amdgpu_discovery
+----------------
+
+Provides raw access to the IP discovery binary provided by the GPU.  Read this
+file to access the raw binary.  This is useful for verifying the contents of
+the IP discovery table.  It is chip specific.
+
+amdgpu_vbios
+------------
+
+Provides raw access to the ROM binary image from the GPU.  Read this file to
+access the raw binary.  This is useful for verifying the contents of the
+video BIOS ROM.  It is board specific.
+
+amdgpu_evict_gtt
+----------------
+
+Evict all buffers from the GTT memory pool.  Read this file to evict all
+buffers from this pool.
+
+amdgpu_evict_vram
+-----------------
+
+Evict all buffers from the VRAM memory pool.  Read this file to evict all
+buffers from this pool.
+
+amdgpu_gpu_recover
+------------------
+
+Trigger a GPU reset.  Read this file to trigger reset the entire GPU.
+All work currently running  on the GPU will be lost.
+
+amdgpu_ring_<name>
+------------------
+
+Provides read access to the kernel managed ring buffers for each ring <name>.
+These are useful for debugging problems on a particular ring.  The ring buffer
+is how the CPU sends commands to the GPU.  The CPU writes commands into the
+buffer and then asks the GPU engine to process it.  This is the raw binary
+contents of the ring buffer.  Use a tool like UMR to decode the rings into human
+readable form.
+
+amdgpu_mqd_<name>
+-----------------
+
+Provides read access to the kernel managed MQD (Memory Queue Descriptor) for
+ring <name> managed by the kernel driver.  MQDs define the features of the ring
+and are used to store the ring's state when it is not connected to hardware.
+The driver writes the requested ring features and metadata (GPU addresses of
+the ring itself and associated buffers) to the MQD and the firmware uses the MQD
+to populate the hardware when the ring is mapped to a hardware slot.  Only
+available on engines which use MQDs.  This provides access to the raw MQD
+binary.
+
+amdgpu_error_<name>
+-------------------
+
+Provides an interface to set an error code on the dma fences associated with
+ring <name>.  The error code specified is propagated to all fences associated
+with the ring.  Use this to inject a fence error into a ring.
+
+amdgpu_pm_info
+--------------
+
+Provides human readable information about the power management features
+and state of the GPU.  This includes current GFX clock, Memory clock,
+voltages, average SoC power, temperature, GFX load, Memory load, SMU
+feature mask, VCN power state, clock and power gating features.
+
+amdgpu_firmware_info
+--------------------
+
+Lists the firmware versions for all firmwares used by the GPU.  Only
+entries with a non-0 version are valid.  If the version is 0, the firmware
+is not valid for the GPU.
+
+amdgpu_fence_info
+-----------------
+
+Shows the last signalled and emitted fence sequence numbers for each
+kernel driver managed ring.  Fences are associated with submissions
+to the engine.  Emitted fences have been submitted to the ring
+and signalled fences have been signalled by the GPU.  Rings with a
+larger emitted fence value have outstanding work that is still being
+processed by the engine that owns that ring.  When the emitted and
+signalled fence values are equal, the ring is idle.
+
+amdgpu_gem_info
+---------------
+
+Lists all of the PIDs using the GPU and the GPU buffers that they have
+allocated.  This lists the buffer size, pool (VRAM, GTT, etc.), and buffer
+attributes (CPU access required, CPU cache attributes, etc.).
+
+amdgpu_vm_info
+--------------
+
+Lists all of the PIDs using the GPU and the GPU buffers that they have
+allocated as well as the status of those buffers relative to that process'
+GPU virtual address space (e.g., evicted, idle, invalidated, etc.).
+
+amdgpu_sa_info
+--------------
+
+Prints out all of the suballocations (sa) by the suballocation manager in the
+kernel driver.  Prints the GPU address, size, and fence info associated
+with each suballocation.  The suballocations are used internally within
+the kernel driver for various things.
+
+amdgpu_<pool>_mm
+----------------
+
+Prints TTM information about the memory pool <pool>.
+
+amdgpu_vram
+-----------
+
+Provides direct access to VRAM.  Used by tools like UMR to inspect
+objects in VRAM.
+
+amdgpu_iomem
+------------
+
+Provides direct access to GTT memory.  Used by tools like UMR to inspect
+GTT memory.
+
+amdgpu_regs_*
+-------------
+
+Provides direct access to various register apertures on the GPU.  Used
+by tools like UMR to access GPU registers.
+
+amdgpu_regs2
+------------
+
+Provides an IOCTL interface used by UMR for interacting with GPU registers.
+
+
+amdgpu_sensors
+--------------
+
+Provides an interface to query GPU power metrics (temperature, average
+power, etc.).  Used by tools like UMR to query GPU power metrics.
+
+
+amdgpu_gca_config
+-----------------
+
+Provides an interface to query GPU details (Graphics/Compute Array config,
+PCI config, GPU family, etc.).  Used by tools like UMR to query GPU details.
+
+amdgpu_wave
+-----------
+
+Used to query GFX/compute wave information from the hardware.  Used by tools
+like UMR to query GFX/compute wave information.
+
+amdgpu_gpr
+----------
+
+Used to query GFX/compute GPR (General Purpose Register) information from the
+hardware.  Used by tools like UMR to query GPRs when debugging shaders.
+
+amdgpu_gprwave
+--------------
+
+Provides an IOCTL interface used by UMR for interacting with shader waves.
+
+amdgpu_fw_attestation
+---------------------
+
+Provides an interface for reading back firmware attestation records.