sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 127 insertions, 0 deletions

diff --git a/rust/syn/file.rs b/rust/syn/file.rs
new file mode 100644
index 000000000..ce2d2680c
--- /dev/null
+++ b/rust/syn/file.rs
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use crate::attr::Attribute;
+use crate::item::Item;
+
+ast_struct! {
+    /// A complete file of Rust source code.
+    ///
+    /// Typically `File` objects are created with [`parse_file`].
+    ///
+    /// [`parse_file`]: crate::parse_file
+    ///
+    /// # Example
+    ///
+    /// Parse a Rust source file into a `syn::File` and print out a debug
+    /// representation of the syntax tree.
+    ///
+    /// ```
+    /// use std::env;
+    /// use std::fs;
+    /// use std::process;
+    ///
+    /// fn main() {
+    /// # }
+    /// #
+    /// # fn fake_main() {
+    ///     let mut args = env::args();
+    ///     let _ = args.next(); // executable name
+    ///
+    ///     let filename = match (args.next(), args.next()) {
+    ///         (Some(filename), None) => filename,
+    ///         _ => {
+    ///             eprintln!("Usage: dump-syntax path/to/filename.rs");
+    ///             process::exit(1);
+    ///         }
+    ///     };
+    ///
+    ///     let src = fs::read_to_string(&filename).expect("unable to read file");
+    ///     let syntax = syn::parse_file(&src).expect("unable to parse file");
+    ///
+    ///     // Debug impl is available if Syn is built with "extra-traits" feature.
+    ///     println!("{:#?}", syntax);
+    /// }
+    /// ```
+    ///
+    /// Running with its own source code as input, this program prints output
+    /// that begins with:
+    ///
+    /// ```text
+    /// File {
+    ///     shebang: None,
+    ///     attrs: [],
+    ///     items: [
+    ///         Use(
+    ///             ItemUse {
+    ///                 attrs: [],
+    ///                 vis: Inherited,
+    ///                 use_token: Use,
+    ///                 leading_colon: None,
+    ///                 tree: Path(
+    ///                     UsePath {
+    ///                         ident: Ident(
+    ///                             std,
+    ///                         ),
+    ///                         colon2_token: Colon2,
+    ///                         tree: Name(
+    ///                             UseName {
+    ///                                 ident: Ident(
+    ///                                     env,
+    ///                                 ),
+    ///                             },
+    ///                         ),
+    ///                     },
+    ///                 ),
+    ///                 semi_token: Semi,
+    ///             },
+    ///         ),
+    /// ...
+    /// ```
+    #[cfg_attr(docsrs, doc(cfg(feature = "full")))]
+    pub struct File {
+        pub shebang: Option<String>,
+        pub attrs: Vec<Attribute>,
+        pub items: Vec<Item>,
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use crate::attr::Attribute;
+    use crate::error::Result;
+    use crate::file::File;
+    use crate::parse::{Parse, ParseStream};
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for File {
+        fn parse(input: ParseStream) -> Result<Self> {
+            Ok(File {
+                shebang: None,
+                attrs: input.call(Attribute::parse_inner)?,
+                items: {
+                    let mut items = Vec::new();
+                    while !input.is_empty() {
+                        items.push(input.parse()?);
+                    }
+                    items
+                },
+            })
+        }
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use crate::attr::FilterAttrs;
+    use crate::file::File;
+    use proc_macro2::TokenStream;
+    use quote::{ToTokens, TokenStreamExt};
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
+    impl ToTokens for File {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            tokens.append_all(self.attrs.inner());
+            tokens.append_all(&self.items);
+        }
+    }
+}