Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

1 files changed, 105 insertions, 0 deletions

diff --git a/rust/macros/vtable.rs b/rust/macros/vtable.rs
new file mode 100644
index 000000000..c6510b0c4
--- /dev/null
+++ b/rust/macros/vtable.rs
@@ -0,0 +1,105 @@
+// 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: ();
+    });
+
+    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_consts = HashSet::new();
+
+    // Iterate over all user-defined constants to gather any possible explicit overrides.
+    for item in &item.items {
+        if let ImplItem::Const(const_item) = item {
+            defined_consts.insert(const_item.ident.clone());
+        }
+    }
+
+    gen_items.push(parse_quote! {
+        const USE_VTABLE_ATTR: () = ();
+    });
+
+    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_consts.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",
+        ))?,
+    }
+}