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, 37 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/zero.rst b/Documentation/admin-guide/device-mapper/zero.rst
new file mode 100644
index 000000000..11fb5cf45
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/zero.rst
@@ -0,0 +1,37 @@
+=======
+dm-zero
+=======
+
+Device-Mapper's "zero" target provides a block-device that always returns
+zero'd data on reads and silently drops writes. This is similar behavior to
+/dev/zero, but as a block-device instead of a character-device.
+
+Dm-zero has no target-specific parameters.
+
+One very interesting use of dm-zero is for creating "sparse" devices in
+conjunction with dm-snapshot. A sparse device reports a device-size larger
+than the amount of actual storage space available for that device. A user can
+write data anywhere within the sparse device and read it back like a normal
+device. Reads to previously unwritten areas will return a zero'd buffer. When
+enough data has been written to fill up the actual storage space, the sparse
+device is deactivated. This can be very useful for testing device and
+filesystem limitations.
+
+To create a sparse device, start by creating a dm-zero device that's the
+desired size of the sparse device. For this example, we'll assume a 10TB
+sparse device::
+
+  TEN_TERABYTES=`expr 10 \* 1024 \* 1024 \* 1024 \* 2`   # 10 TB in sectors
+  echo "0 $TEN_TERABYTES zero" | dmsetup create zero1
+
+Then create a snapshot of the zero device, using any available block-device as
+the COW device. The size of the COW device will determine the amount of real
+space available to the sparse device. For this example, we'll assume /dev/sdb1
+is an available 10GB partition::
+
+  echo "0 $TEN_TERABYTES snapshot /dev/mapper/zero1 /dev/sdb1 p 128" | \
+     dmsetup create sparse1
+
+This will create a 10TB sparse device called /dev/mapper/sparse1 that has
+10GB of actual storage space available. If more than 10GB of data is written
+to this device, it will start returning I/O errors.