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, 136 insertions, 0 deletions

diff --git a/Documentation/tools/rtla/rtla-timerlat-top.rst b/Documentation/tools/rtla/rtla-timerlat-top.rst
new file mode 100644
index 000000000..05959f1a4
--- /dev/null
+++ b/Documentation/tools/rtla/rtla-timerlat-top.rst
@@ -0,0 +1,136 @@
+.. |tool| replace:: timerlat top
+
+====================
+rtla-timerlat-top
+====================
+-------------------------------------------
+Measures the operating system timer latency
+-------------------------------------------
+
+:Manual section: 1
+
+SYNOPSIS
+========
+**rtla timerlat top** [*OPTIONS*] ...
+
+DESCRIPTION
+===========
+
+.. include:: common_timerlat_description.txt
+
+The **rtla timerlat top** displays a summary of the periodic output
+from the *timerlat* tracer. It also provides information for each
+operating system noise via the **osnoise:** tracepoints that can be
+seen with the option **-T**.
+
+OPTIONS
+=======
+
+.. include:: common_timerlat_options.txt
+
+.. include:: common_top_options.txt
+
+.. include:: common_options.txt
+
+.. include:: common_timerlat_aa.txt
+
+**--aa-only** *us*
+
+        Set stop tracing conditions and run without collecting and displaying statistics.
+        Print the auto-analysis if the system hits the stop tracing condition. This option
+        is useful to reduce rtla timerlat CPU, enabling the debug without the overhead of
+        collecting the statistics.
+
+EXAMPLE
+=======
+
+In the example below, the timerlat tracer is dispatched in cpus *1-23* in the
+automatic trace mode, instructing the tracer to stop if a *40 us* latency or
+higher is found::
+
+  # timerlat -a 40 -c 1-23 -q
+                                     Timer Latency
+    0 00:00:12   |          IRQ Timer Latency (us)        |         Thread Timer Latency (us)
+  CPU COUNT      |      cur       min       avg       max |      cur       min       avg       max
+    1 #12322     |        0         0         1        15 |       10         3         9        31
+    2 #12322     |        3         0         1        12 |       10         3         9        23
+    3 #12322     |        1         0         1        21 |        8         2         8        34
+    4 #12322     |        1         0         1        17 |       10         2        11        33
+    5 #12322     |        0         0         1        12 |        8         3         8        25
+    6 #12322     |        1         0         1        14 |       16         3        11        35
+    7 #12322     |        0         0         1        14 |        9         2         8        29
+    8 #12322     |        1         0         1        22 |        9         3         9        34
+    9 #12322     |        0         0         1        14 |        8         2         8        24
+   10 #12322     |        1         0         0        12 |        9         3         8        24
+   11 #12322     |        0         0         0        15 |        6         2         7        29
+   12 #12321     |        1         0         0        13 |        5         3         8        23
+   13 #12319     |        0         0         1        14 |        9         3         9        26
+   14 #12321     |        1         0         0        13 |        6         2         8        24
+   15 #12321     |        1         0         1        15 |       12         3        11        27
+   16 #12318     |        0         0         1        13 |        7         3        10        24
+   17 #12319     |        0         0         1        13 |       11         3         9        25
+   18 #12318     |        0         0         0        12 |        8         2         8        20
+   19 #12319     |        0         0         1        18 |       10         2         9        28
+   20 #12317     |        0         0         0        20 |        9         3         8        34
+   21 #12318     |        0         0         0        13 |        8         3         8        28
+   22 #12319     |        0         0         1        11 |        8         3        10        22
+   23 #12320     |       28         0         1        28 |       41         3        11        41
+  rtla timerlat hit stop tracing
+  ## CPU 23 hit stop tracing, analyzing it ##
+  IRQ handler delay:                                        27.49 us (65.52 %)
+  IRQ latency:                                              28.13 us
+  Timerlat IRQ duration:                                     9.59 us (22.85 %)
+  Blocking thread:                                           3.79 us (9.03 %)
+                         objtool:49256                       3.79 us
+    Blocking thread stacktrace
+                -> timerlat_irq
+                -> __hrtimer_run_queues
+                -> hrtimer_interrupt
+                -> __sysvec_apic_timer_interrupt
+                -> sysvec_apic_timer_interrupt
+                -> asm_sysvec_apic_timer_interrupt
+                -> _raw_spin_unlock_irqrestore
+                -> cgroup_rstat_flush_locked
+                -> cgroup_rstat_flush_irqsafe
+                -> mem_cgroup_flush_stats
+                -> mem_cgroup_wb_stats
+                -> balance_dirty_pages
+                -> balance_dirty_pages_ratelimited_flags
+                -> btrfs_buffered_write
+                -> btrfs_do_write_iter
+                -> vfs_write
+                -> __x64_sys_pwrite64
+                -> do_syscall_64
+                -> entry_SYSCALL_64_after_hwframe
+  ------------------------------------------------------------------------
+    Thread latency:                                          41.96 us (100%)
+
+  The system has exit from idle latency!
+    Max timerlat IRQ latency from idle: 17.48 us in cpu 4
+  Saving trace to timerlat_trace.txt
+
+In this case, the major factor was the delay suffered by the *IRQ handler*
+that handles **timerlat** wakeup: *65.52%*. This can be caused by the
+current thread masking interrupts, which can be seen in the blocking
+thread stacktrace: the current thread (*objtool:49256*) disabled interrupts
+via *raw spin lock* operations inside mem cgroup, while doing write
+syscall in a btrfs file system.
+
+The raw trace is saved in the **timerlat_trace.txt** file for further analysis.
+
+Note that **rtla timerlat** was dispatched without changing *timerlat* tracer
+threads' priority. That is generally not needed because these threads have
+priority *FIFO:95* by default, which is a common priority used by real-time
+kernel developers to analyze scheduling delays.
+
+SEE ALSO
+--------
+**rtla-timerlat**\(1), **rtla-timerlat-hist**\(1)
+
+`Timerlat tracer <https://docs.kernel.org/trace/timerlat-tracer.html>`__
+
+AUTHOR
+------
+Written by Daniel Bristot de Oliveira <bristot@kernel.org>
+
+.. include:: common_appendix.txt