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, 136 insertions, 0 deletions

diff --git a/rust/zerocopy-derive/derive/mod.rs b/rust/zerocopy-derive/derive/mod.rs
new file mode 100644
index 000000000..b3839fcf7
--- /dev/null
+++ b/rust/zerocopy-derive/derive/mod.rs
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: (BSD-2-Clause OR Apache-2.0) OR MIT
+//
+pub mod from_bytes;
+pub mod into_bytes;
+pub mod known_layout;
+pub mod try_from_bytes;
+pub mod unaligned;
+
+use proc_macro2::{Span, TokenStream};
+use quote::quote;
+use syn::{Data, Error};
+
+use crate::{
+    repr::StructUnionRepr,
+    util::{Ctx, DataExt, FieldBounds, ImplBlockBuilder, Trait},
+};
+
+pub(crate) fn derive_immutable(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
+    Ok(match &ctx.ast.data {
+        Data::Struct(strct) => {
+            ImplBlockBuilder::new(ctx, strct, Trait::Immutable, FieldBounds::ALL_SELF).build()
+        }
+        Data::Enum(enm) => {
+            ImplBlockBuilder::new(ctx, enm, Trait::Immutable, FieldBounds::ALL_SELF).build()
+        }
+        Data::Union(unn) => {
+            ImplBlockBuilder::new(ctx, unn, Trait::Immutable, FieldBounds::ALL_SELF).build()
+        }
+    })
+}
+
+pub(crate) fn derive_hash(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
+    // This doesn't delegate to `impl_block` because `impl_block` assumes it is
+    // deriving a `zerocopy`-defined trait, and these trait impls share a common
+    // shape that `Hash` does not. In particular, `zerocopy` traits contain a
+    // method that only `zerocopy_derive` macros are supposed to implement, and
+    // `impl_block` generating this trait method is incompatible with `Hash`.
+    let type_ident = &ctx.ast.ident;
+    let (impl_generics, ty_generics, where_clause) = ctx.ast.generics.split_for_impl();
+    let where_predicates = where_clause.map(|clause| &clause.predicates);
+    let zerocopy_crate = &ctx.zerocopy_crate;
+    let core = ctx.core_path();
+    Ok(quote! {
+        impl #impl_generics #core::hash::Hash for #type_ident #ty_generics
+        where
+            Self: #zerocopy_crate::IntoBytes + #zerocopy_crate::Immutable,
+            #where_predicates
+        {
+            fn hash<H: #core::hash::Hasher>(&self, state: &mut H) {
+                #core::hash::Hasher::write(state, #zerocopy_crate::IntoBytes::as_bytes(self))
+            }
+
+            fn hash_slice<H: #core::hash::Hasher>(data: &[Self], state: &mut H) {
+                #core::hash::Hasher::write(state, #zerocopy_crate::IntoBytes::as_bytes(data))
+            }
+        }
+    })
+}
+
+pub(crate) fn derive_eq(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
+    // This doesn't delegate to `impl_block` because `impl_block` assumes it is
+    // deriving a `zerocopy`-defined trait, and these trait impls share a common
+    // shape that `Eq` does not. In particular, `zerocopy` traits contain a
+    // method that only `zerocopy_derive` macros are supposed to implement, and
+    // `impl_block` generating this trait method is incompatible with `Eq`.
+    let type_ident = &ctx.ast.ident;
+    let (impl_generics, ty_generics, where_clause) = ctx.ast.generics.split_for_impl();
+    let where_predicates = where_clause.map(|clause| &clause.predicates);
+    let zerocopy_crate = &ctx.zerocopy_crate;
+    let core = ctx.core_path();
+    Ok(quote! {
+        impl #impl_generics #core::cmp::PartialEq for #type_ident #ty_generics
+        where
+            Self: #zerocopy_crate::IntoBytes + #zerocopy_crate::Immutable,
+            #where_predicates
+        {
+            fn eq(&self, other: &Self) -> bool {
+                #core::cmp::PartialEq::eq(
+                    #zerocopy_crate::IntoBytes::as_bytes(self),
+                    #zerocopy_crate::IntoBytes::as_bytes(other),
+                )
+            }
+        }
+
+        impl #impl_generics #core::cmp::Eq for #type_ident #ty_generics
+        where
+            Self: #zerocopy_crate::IntoBytes + #zerocopy_crate::Immutable,
+            #where_predicates
+        {
+        }
+    })
+}
+
+pub(crate) fn derive_split_at(ctx: &Ctx, _top_level: Trait) -> Result<TokenStream, Error> {
+    let repr = StructUnionRepr::from_attrs(&ctx.ast.attrs)?;
+
+    match &ctx.ast.data {
+        Data::Struct(_) => {}
+        Data::Enum(_) | Data::Union(_) => {
+            return ctx
+                .error_or_skip(Error::new(Span::call_site(), "can only be applied to structs"));
+        }
+    };
+
+    if repr.get_packed().is_some() {
+        return ctx.error_or_skip(Error::new(
+            Span::call_site(),
+            "must not have #[repr(packed)] attribute",
+        ));
+    }
+
+    if !(repr.is_c() || repr.is_transparent()) {
+        return ctx.error_or_skip(Error::new(
+            Span::call_site(),
+            "must have #[repr(C)] or #[repr(transparent)] in order to guarantee this type's layout is splitable",
+        ));
+    }
+
+    let fields = ctx.ast.data.fields();
+    let trailing_field = if let Some(((_, _, trailing_field), _)) = fields.split_last() {
+        trailing_field
+    } else {
+        return ctx.error_or_skip(Error::new(Span::call_site(), "must at least one field"));
+    };
+
+    let zerocopy_crate = &ctx.zerocopy_crate;
+    // SAFETY: `#ty`, per the above checks, is `repr(C)` or `repr(transparent)`
+    // and is not packed; its trailing field is guaranteed to be well-aligned
+    // for its type. By invariant on `FieldBounds::TRAILING_SELF`, the trailing
+    // slice of the trailing field is also well-aligned for its type.
+    Ok(ImplBlockBuilder::new(ctx, &ctx.ast.data, Trait::SplitAt, FieldBounds::TRAILING_SELF)
+        .inner_extras(quote! {
+            type Elem = <#trailing_field as #zerocopy_crate::SplitAt>::Elem;
+        })
+        .build())
+}