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, 34 insertions, 0 deletions

diff --git a/Documentation/filesystems/ext4/bigalloc.rst b/Documentation/filesystems/ext4/bigalloc.rst
new file mode 100644
index 000000000..976a180b2
--- /dev/null
+++ b/Documentation/filesystems/ext4/bigalloc.rst
@@ -0,0 +1,34 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Bigalloc
+--------
+
+At the moment, the default size of a block is 4KiB, which is a commonly
+supported page size on most MMU-capable hardware. This is fortunate, as
+ext4 code is not prepared to handle the case where the block size
+exceeds the page size. However, for a filesystem of mostly huge files,
+it is desirable to be able to allocate disk blocks in units of multiple
+blocks to reduce both fragmentation and metadata overhead. The
+bigalloc feature provides exactly this ability.
+
+The bigalloc feature (EXT4_FEATURE_RO_COMPAT_BIGALLOC) changes ext4 to
+use clustered allocation, so that each bit in the ext4 block allocation
+bitmap addresses a power of two number of blocks. For example, if the
+file system is mainly going to be storing large files in the 4-32
+megabyte range, it might make sense to set a cluster size of 1 megabyte.
+This means that each bit in the block allocation bitmap now addresses
+256 4k blocks. This shrinks the total size of the block allocation
+bitmaps for a 2T file system from 64 megabytes to 256 kilobytes. It also
+means that a block group addresses 32 gigabytes instead of 128 megabytes,
+also shrinking the amount of file system overhead for metadata.
+
+The administrator can set a block cluster size at mkfs time (which is
+stored in the s_log_cluster_size field in the superblock); from then
+on, the block bitmaps track clusters, not individual blocks. This means
+that block groups can be several gigabytes in size (instead of just
+128MiB); however, the minimum allocation unit becomes a cluster, not a
+block, even for directories. TaoBao had a patchset to extend the “use
+units of clusters instead of blocks” to the extent tree, though it is
+not clear where those patches went-- they eventually morphed into
+“extent tree v2” but that code has not landed as of May 2015.
+