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, 60 insertions, 0 deletions

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
new file mode 100644
index 000000000..d18fbf4da
--- /dev/null
+++ b/rust/macros/helpers.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{
+    parse::{
+        Parse,
+        ParseStream, //
+    },
+    Attribute,
+    Error,
+    LitStr,
+    Result, //
+};
+
+/// A string literal that is required to have ASCII value only.
+pub(crate) struct AsciiLitStr(LitStr);
+
+impl Parse for AsciiLitStr {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let s: LitStr = input.parse()?;
+        if !s.value().is_ascii() {
+            return Err(Error::new_spanned(s, "expected ASCII-only string literal"));
+        }
+        Ok(Self(s))
+    }
+}
+
+impl ToTokens for AsciiLitStr {
+    fn to_tokens(&self, ts: &mut TokenStream) {
+        self.0.to_tokens(ts);
+    }
+}
+
+impl AsciiLitStr {
+    pub(crate) fn value(&self) -> String {
+        self.0.value()
+    }
+}
+
+pub(crate) fn file() -> String {
+    #[cfg(not(CONFIG_RUSTC_HAS_SPAN_FILE))]
+    {
+        proc_macro::Span::call_site()
+            .source_file()
+            .path()
+            .to_string_lossy()
+            .into_owned()
+    }
+
+    #[cfg(CONFIG_RUSTC_HAS_SPAN_FILE)]
+    {
+        proc_macro::Span::call_site().file()
+    }
+}
+
+/// Obtain all `#[cfg]` attributes.
+pub(crate) fn gather_cfg_attrs(attr: &[Attribute]) -> impl Iterator<Item = &Attribute> + '_ {
+    attr.iter().filter(|a| a.path().is_ident("cfg"))
+}