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, 96 insertions, 0 deletions

diff --git a/rust/macros/fmt.rs b/rust/macros/fmt.rs
new file mode 100644
index 000000000..ce6c72493
--- /dev/null
+++ b/rust/macros/fmt.rs
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use std::collections::BTreeSet;
+
+use proc_macro2::{Ident, TokenStream, TokenTree};
+use quote::quote_spanned;
+
+/// Please see [`crate::fmt`] for documentation.
+pub(crate) fn fmt(input: TokenStream) -> TokenStream {
+    let mut input = input.into_iter();
+
+    let first_opt = input.next();
+    let first_owned_str;
+    let mut names = BTreeSet::new();
+    let first_span = {
+        let Some((mut first_str, first_span)) = (match first_opt.as_ref() {
+            Some(TokenTree::Literal(first_lit)) => {
+                first_owned_str = first_lit.to_string();
+                Some(first_owned_str.as_str()).and_then(|first| {
+                    let first = first.strip_prefix('"')?;
+                    let first = first.strip_suffix('"')?;
+                    Some((first, first_lit.span()))
+                })
+            }
+            _ => None,
+        }) else {
+            return first_opt.into_iter().chain(input).collect();
+        };
+
+        // Parse `identifier`s from the format string.
+        //
+        // See https://doc.rust-lang.org/std/fmt/index.html#syntax.
+        while let Some((_, rest)) = first_str.split_once('{') {
+            first_str = rest;
+            if let Some(rest) = first_str.strip_prefix('{') {
+                first_str = rest;
+                continue;
+            }
+            if let Some((name, rest)) = first_str.split_once('}') {
+                first_str = rest;
+                let name = name.split_once(':').map_or(name, |(name, _)| name);
+                if !name.is_empty() && !name.chars().all(|c| c.is_ascii_digit()) {
+                    names.insert(name);
+                }
+            }
+        }
+        first_span
+    };
+
+    let adapter = quote_spanned!(first_span => ::kernel::fmt::Adapter);
+
+    let mut args = TokenStream::from_iter(first_opt);
+    {
+        let mut flush = |args: &mut TokenStream, current: &mut TokenStream| {
+            let current = std::mem::take(current);
+            if !current.is_empty() {
+                let (lhs, rhs) = (|| {
+                    let mut current = current.into_iter();
+                    let mut acc = TokenStream::new();
+                    while let Some(tt) = current.next() {
+                        // Split on `=` only once to handle cases like `a = b = c`.
+                        if matches!(&tt, TokenTree::Punct(p) if p.as_char() == '=') {
+                            names.remove(acc.to_string().as_str());
+                            // Include the `=` itself to keep the handling below uniform.
+                            acc.extend([tt]);
+                            return (Some(acc), current.collect::<TokenStream>());
+                        }
+                        acc.extend([tt]);
+                    }
+                    (None, acc)
+                })();
+                args.extend(quote_spanned!(first_span => #lhs #adapter(&(#rhs))));
+            }
+        };
+
+        let mut current = TokenStream::new();
+        for tt in input {
+            match &tt {
+                TokenTree::Punct(p) if p.as_char() == ',' => {
+                    flush(&mut args, &mut current);
+                    &mut args
+                }
+                _ => &mut current,
+            }
+            .extend([tt]);
+        }
+        flush(&mut args, &mut current);
+    }
+
+    for name in names {
+        let name = Ident::new(name, first_span);
+        args.extend(quote_spanned!(first_span => , #name = #adapter(&#name)));
+    }
+
+    quote_spanned!(first_span => ::core::format_args!(#args))
+}