selftests/bpf: Add a test for objects stuck in free_by_rcu_ttracegrafted

Delete all elements of BPF_F_NO_PREALLOC hash map in one batch. The first
free_bulk() starts RCU tasks trace GP and the rest of the elements are
freed while it's in flight. Wait for call_rcu_ttrace_in_progress to clear
in bpf_mem_cache of every cpu and check that free_by_rcu_ttrace and
waiting_for_gp_ttrace lists are empty.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20260930095920.601738-4-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 136 insertions, 0 deletions

diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
new file mode 100644
index 000000000..be9a5ed8a
--- /dev/null
+++ b/rust/macros/vtable.rs
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use std::{
+    collections::HashSet,
+    iter::Extend, //
+};
+
+use proc_macro2::{
+    Ident,
+    TokenStream, //
+};
+use quote::ToTokens;
+use syn::{
+    parse_quote,
+    Error,
+    ImplItem,
+    Item,
+    ItemImpl,
+    ItemTrait,
+    Result,
+    TraitItem, //
+};
+
+fn handle_trait(mut item: ItemTrait) -> Result<ItemTrait> {
+    let mut gen_items = Vec::new();
+
+    gen_items.push(parse_quote! {
+         /// A marker to prevent implementors from forgetting to use [`#[vtable]`](vtable)
+         /// attribute when implementing this trait.
+         const USE_VTABLE_ATTR: ();
+    });
+
+    // Add `type OwnerModule: ModuleMetadata` as a required associated type if
+    // the trait does not already define it.
+    if !item
+        .items
+        .iter()
+        .any(|i| matches!(i, TraitItem::Type(t) if t.ident == "OwnerModule"))
+    {
+        gen_items.push(parse_quote! {
+            /// The module implementing this vtable trait.
+            ///
+            /// Automatically set to `crate::LocalModule` by the `#[vtable]`
+            /// impl macro.
+            type OwnerModule: ::kernel::ModuleMetadata;
+        });
+    }
+
+    for item in &item.items {
+        if let TraitItem::Fn(fn_item) = item {
+            let name = &fn_item.sig.ident;
+            let gen_const_name = Ident::new(
+                &format!("HAS_{}", name.to_string().to_uppercase()),
+                name.span(),
+            );
+
+            // We don't know on the implementation-site whether a method is required or provided
+            // so we have to generate a const for all methods.
+            let cfg_attrs = crate::helpers::gather_cfg_attrs(&fn_item.attrs);
+            let comment =
+                format!("Indicates if the `{name}` method is overridden by the implementor.");
+            gen_items.push(parse_quote! {
+                #(#cfg_attrs)*
+                #[doc = #comment]
+                const #gen_const_name: bool = false;
+            });
+        }
+    }
+
+    item.items.extend(gen_items);
+    Ok(item)
+}
+
+fn handle_impl(mut item: ItemImpl) -> Result<ItemImpl> {
+    let mut gen_items = Vec::new();
+    let mut defined_items = HashSet::new();
+
+    // Iterate over all user-defined items to gather any possible explicit overrides.
+    for item in &item.items {
+        match item {
+            ImplItem::Const(const_item) => {
+                defined_items.insert(const_item.ident.clone());
+            }
+            ImplItem::Type(type_item) => {
+                defined_items.insert(type_item.ident.clone());
+            }
+            _ => {}
+        }
+    }
+
+    gen_items.push(parse_quote! {
+        const USE_VTABLE_ATTR: () = ();
+    });
+
+    // Auto-insert `type OwnerModule = crate::LocalModule` if not explicitly defined.
+    // `crate::LocalModule` resolves to the real module type (via `module!`) or a
+    // dummy fallback in non-module contexts (e.g., doctests).
+    if !defined_items.contains(&parse_quote!(OwnerModule)) {
+        gen_items.push(parse_quote! {
+            type OwnerModule = crate::LocalModule;
+        });
+    }
+
+    for item in &item.items {
+        if let ImplItem::Fn(fn_item) = item {
+            let name = &fn_item.sig.ident;
+            let gen_const_name = Ident::new(
+                &format!("HAS_{}", name.to_string().to_uppercase()),
+                name.span(),
+            );
+            // Skip if it's declared already -- this allows user override.
+            if defined_items.contains(&gen_const_name) {
+                continue;
+            }
+            let cfg_attrs = crate::helpers::gather_cfg_attrs(&fn_item.attrs);
+            gen_items.push(parse_quote! {
+                #(#cfg_attrs)*
+                const #gen_const_name: bool = true;
+            });
+        }
+    }
+
+    item.items.extend(gen_items);
+    Ok(item)
+}
+
+pub(crate) fn vtable(input: Item) -> Result<TokenStream> {
+    match input {
+        Item::Trait(item) => Ok(handle_trait(item)?.into_token_stream()),
+        Item::Impl(item) => Ok(handle_impl(item)?.into_token_stream()),
+        _ => Err(Error::new_spanned(
+            input,
+            "`#[vtable]` attribute should only be applied to trait or impl block",
+        ))?,
+    }
+}