x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 169 insertions, 0 deletions

diff --git a/Documentation/locking/locktorture.rst b/Documentation/locking/locktorture.rst
new file mode 100644
index 000000000..3e763f77a
--- /dev/null
+++ b/Documentation/locking/locktorture.rst
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+==================================
+Kernel Lock Torture Test Operation
+==================================
+
+CONFIG_LOCK_TORTURE_TEST
+========================
+
+The CONFIG_LOCK_TORTURE_TEST config option provides a kernel module
+that runs torture tests on core kernel locking primitives. The kernel
+module, 'locktorture', may be built after the fact on the running
+kernel to be tested, if desired. The tests periodically output status
+messages via printk(), which can be examined via the dmesg (perhaps
+grepping for "torture").  The test is started when the module is loaded,
+and stops when the module is unloaded. This program is based on how RCU
+is tortured, via rcutorture.
+
+This torture test consists of creating a number of kernel threads which
+acquire the lock and hold it for specific amount of time, thus simulating
+different critical region behaviors. The amount of contention on the lock
+can be simulated by either enlarging this critical region hold time and/or
+creating more kthreads.
+
+
+Module Parameters
+=================
+
+This module has the following parameters:
+
+
+Locktorture-specific
+--------------------
+
+nwriters_stress
+		  Number of kernel threads that will stress exclusive lock
+		  ownership (writers). The default value is twice the number
+		  of online CPUs.
+
+nreaders_stress
+		  Number of kernel threads that will stress shared lock
+		  ownership (readers). The default is the same amount of writer
+		  locks. If the user did not specify nwriters_stress, then
+		  both readers and writers be the amount of online CPUs.
+
+torture_type
+		  Type of lock to torture. By default, only spinlocks will
+		  be tortured. This module can torture the following locks,
+		  with string values as follows:
+
+		     - "lock_busted":
+				Simulates a buggy lock implementation.
+
+		     - "spin_lock":
+				spin_lock() and spin_unlock() pairs.
+
+		     - "spin_lock_irq":
+				spin_lock_irq() and spin_unlock_irq() pairs.
+
+		     - "rw_lock":
+				read/write lock() and unlock() rwlock pairs.
+
+		     - "rw_lock_irq":
+				read/write lock_irq() and unlock_irq()
+				rwlock pairs.
+
+		     - "mutex_lock":
+				mutex_lock() and mutex_unlock() pairs.
+
+		     - "rtmutex_lock":
+				rtmutex_lock() and rtmutex_unlock() pairs.
+				Kernel must have CONFIG_RT_MUTEXES=y.
+
+		     - "rwsem_lock":
+				read/write down() and up() semaphore pairs.
+
+
+Torture-framework (RCU + locking)
+---------------------------------
+
+shutdown_secs
+		  The number of seconds to run the test before terminating
+		  the test and powering off the system.  The default is
+		  zero, which disables test termination and system shutdown.
+		  This capability is useful for automated testing.
+
+onoff_interval
+		  The number of seconds between each attempt to execute a
+		  randomly selected CPU-hotplug operation.  Defaults
+		  to zero, which disables CPU hotplugging.  In
+		  CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently
+		  refuse to do any CPU-hotplug operations regardless of
+		  what value is specified for onoff_interval.
+
+onoff_holdoff
+		  The number of seconds to wait until starting CPU-hotplug
+		  operations.  This would normally only be used when
+		  locktorture was built into the kernel and started
+		  automatically at boot time, in which case it is useful
+		  in order to avoid confusing boot-time code with CPUs
+		  coming and going. This parameter is only useful if
+		  CONFIG_HOTPLUG_CPU is enabled.
+
+stat_interval
+		  Number of seconds between statistics-related printk()s.
+		  By default, locktorture will report stats every 60 seconds.
+		  Setting the interval to zero causes the statistics to
+		  be printed -only- when the module is unloaded.
+
+stutter
+		  The length of time to run the test before pausing for this
+		  same period of time.  Defaults to "stutter=5", so as
+		  to run and pause for (roughly) five-second intervals.
+		  Specifying "stutter=0" causes the test to run continuously
+		  without pausing.
+
+shuffle_interval
+		  The number of seconds to keep the test threads affinitized
+		  to a particular subset of the CPUs, defaults to 3 seconds.
+		  Used in conjunction with test_no_idle_hz.
+
+verbose
+		  Enable verbose debugging printing, via printk(). Enabled
+		  by default. This extra information is mostly related to
+		  high-level errors and reports from the main 'torture'
+		  framework.
+
+
+Statistics
+==========
+
+Statistics are printed in the following format::
+
+  spin_lock-torture: Writes:  Total: 93746064  Max/Min: 0/0   Fail: 0
+     (A)		    (B)		   (C)		  (D)	       (E)
+
+  (A): Lock type that is being tortured -- torture_type parameter.
+
+  (B): Number of writer lock acquisitions. If dealing with a read/write
+       primitive a second "Reads" statistics line is printed.
+
+  (C): Number of times the lock was acquired.
+
+  (D): Min and max number of times threads failed to acquire the lock.
+
+  (E): true/false values if there were errors acquiring the lock. This should
+       -only- be positive if there is a bug in the locking primitive's
+       implementation. Otherwise a lock should never fail (i.e., spin_lock()).
+       Of course, the same applies for (C), above. A dummy example of this is
+       the "lock_busted" type.
+
+Usage
+=====
+
+The following script may be used to torture locks::
+
+	#!/bin/sh
+
+	modprobe locktorture
+	sleep 3600
+	rmmod locktorture
+	dmesg | grep torture:
+
+The output can be manually inspected for the error flag of "!!!".
+One could of course create a more elaborate script that automatically
+checked for such errors.  The "rmmod" command forces a "SUCCESS",
+"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed.  The first
+two are self-explanatory, while the last indicates that while there
+were no locking failures, CPU-hotplug problems were detected.
+
+Also see: Documentation/RCU/torture.rst