ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 113 insertions, 0 deletions

diff --git a/rust/macros/paste.rs b/rust/macros/paste.rs
new file mode 100644
index 000000000..2181e312a
--- /dev/null
+++ b/rust/macros/paste.rs
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro2::{Delimiter, Group, Ident, Spacing, Span, TokenTree};
+
+fn concat_helper(tokens: &[TokenTree]) -> Vec<(String, Span)> {
+    let mut tokens = tokens.iter();
+    let mut segments = Vec::new();
+    let mut span = None;
+    loop {
+        match tokens.next() {
+            None => break,
+            Some(TokenTree::Literal(lit)) => {
+                // Allow us to concat string literals by stripping quotes
+                let mut value = lit.to_string();
+                if value.starts_with('"') && value.ends_with('"') {
+                    value.remove(0);
+                    value.pop();
+                }
+                segments.push((value, lit.span()));
+            }
+            Some(TokenTree::Ident(ident)) => {
+                let mut value = ident.to_string();
+                if value.starts_with("r#") {
+                    value.replace_range(0..2, "");
+                }
+                segments.push((value, ident.span()));
+            }
+            Some(TokenTree::Punct(p)) if p.as_char() == ':' => {
+                let Some(TokenTree::Ident(ident)) = tokens.next() else {
+                    panic!("expected identifier as modifier");
+                };
+
+                let (mut value, sp) = segments.pop().expect("expected identifier before modifier");
+                match ident.to_string().as_str() {
+                    // Set the overall span of concatenated token as current span
+                    "span" => {
+                        assert!(
+                            span.is_none(),
+                            "span modifier should only appear at most once"
+                        );
+                        span = Some(sp);
+                    }
+                    "lower" => value = value.to_lowercase(),
+                    "upper" => value = value.to_uppercase(),
+                    v => panic!("unknown modifier `{v}`"),
+                };
+                segments.push((value, sp));
+            }
+            Some(TokenTree::Group(group)) if group.delimiter() == Delimiter::None => {
+                let tokens = group.stream().into_iter().collect::<Vec<TokenTree>>();
+                segments.append(&mut concat_helper(tokens.as_slice()));
+            }
+            token => panic!("unexpected token in paste segments: {token:?}"),
+        };
+    }
+
+    segments
+}
+
+fn concat(tokens: &[TokenTree], group_span: Span) -> TokenTree {
+    let segments = concat_helper(tokens);
+    let pasted: String = segments.into_iter().map(|x| x.0).collect();
+    TokenTree::Ident(Ident::new(&pasted, group_span))
+}
+
+pub(crate) fn expand(tokens: &mut Vec<TokenTree>) {
+    for token in tokens.iter_mut() {
+        if let TokenTree::Group(group) = token {
+            let delimiter = group.delimiter();
+            let span = group.span();
+            let mut stream: Vec<_> = group.stream().into_iter().collect();
+            // Find groups that looks like `[< A B C D >]`
+            if delimiter == Delimiter::Bracket
+                && stream.len() >= 3
+                && matches!(&stream[0], TokenTree::Punct(p) if p.as_char() == '<')
+                && matches!(&stream[stream.len() - 1], TokenTree::Punct(p) if p.as_char() == '>')
+            {
+                // Replace the group with concatenated token
+                *token = concat(&stream[1..stream.len() - 1], span);
+            } else {
+                // Recursively expand tokens inside the group
+                expand(&mut stream);
+                let mut group = Group::new(delimiter, stream.into_iter().collect());
+                group.set_span(span);
+                *token = TokenTree::Group(group);
+            }
+        }
+    }
+
+    // Path segments cannot contain invisible delimiter group, so remove them if any.
+    for i in (0..tokens.len().saturating_sub(3)).rev() {
+        // Looking for a double colon
+        if matches!(
+            (&tokens[i + 1], &tokens[i + 2]),
+            (TokenTree::Punct(a), TokenTree::Punct(b))
+                if a.as_char() == ':' && a.spacing() == Spacing::Joint && b.as_char() == ':'
+        ) {
+            match &tokens[i + 3] {
+                TokenTree::Group(group) if group.delimiter() == Delimiter::None => {
+                    tokens.splice(i + 3..i + 4, group.stream());
+                }
+                _ => (),
+            }
+
+            match &tokens[i] {
+                TokenTree::Group(group) if group.delimiter() == Delimiter::None => {
+                    tokens.splice(i..i + 1, group.stream());
+                }
+                _ => (),
+            }
+        }
+    }
+}