From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug 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 Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- rust/syn/ext.rs | 138 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 138 insertions(+) create mode 100644 rust/syn/ext.rs (limited to 'rust/syn/ext.rs') diff --git a/rust/syn/ext.rs b/rust/syn/ext.rs new file mode 100644 index 000000000..a9be9af42 --- /dev/null +++ b/rust/syn/ext.rs @@ -0,0 +1,138 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +//! Extension traits to provide parsing methods on foreign types. + +use crate::buffer::Cursor; +use crate::error::Result; +use crate::parse::ParseStream; +use crate::parse::Peek; +use crate::sealed::lookahead; +use crate::token::CustomToken; +use proc_macro2::Ident; + +/// Additional methods for `Ident` not provided by proc-macro2 or libproc_macro. +/// +/// This trait is sealed and cannot be implemented for types outside of Syn. It +/// is implemented only for `proc_macro2::Ident`. +pub trait IdentExt: Sized + private::Sealed { + /// Parses any identifier including keywords. + /// + /// This is useful when parsing macro input which allows Rust keywords as + /// identifiers. + /// + /// # Example + /// + /// ``` + /// use syn::{Error, Ident, Result, Token}; + /// use syn::ext::IdentExt; + /// use syn::parse::ParseStream; + /// + /// mod kw { + /// syn::custom_keyword!(name); + /// } + /// + /// // Parses input that looks like `name = NAME` where `NAME` can be + /// // any identifier. + /// // + /// // Examples: + /// // + /// // name = anything + /// // name = impl + /// fn parse_dsl(input: ParseStream) -> Result { + /// input.parse::()?; + /// input.parse::()?; + /// let name = input.call(Ident::parse_any)?; + /// Ok(name) + /// } + /// ``` + fn parse_any(input: ParseStream) -> Result; + + /// Peeks any identifier including keywords. Usage: + /// `input.peek(Ident::peek_any)` + /// + /// This is different from `input.peek(Ident)` which only returns true in + /// the case of an ident which is not a Rust keyword. + #[allow(non_upper_case_globals)] + const peek_any: private::PeekFn = private::PeekFn; + + /// Strips the raw marker `r#`, if any, from the beginning of an ident. + /// + /// - unraw(`x`) = `x` + /// - unraw(`move`) = `move` + /// - unraw(`r#move`) = `move` + /// + /// # Example + /// + /// In the case of interop with other languages like Python that have a + /// different set of keywords than Rust, we might come across macro input + /// that involves raw identifiers to refer to ordinary variables in the + /// other language with a name that happens to be a Rust keyword. + /// + /// The function below appends an identifier from the caller's input onto a + /// fixed prefix. Without using `unraw()`, this would tend to produce + /// invalid identifiers like `__pyo3_get_r#move`. + /// + /// ``` + /// use proc_macro2::Span; + /// use syn::Ident; + /// use syn::ext::IdentExt; + /// + /// fn ident_for_getter(variable: &Ident) -> Ident { + /// let getter = format!("__pyo3_get_{}", variable.unraw()); + /// Ident::new(&getter, Span::call_site()) + /// } + /// ``` + fn unraw(&self) -> Ident; +} + +impl IdentExt for Ident { + fn parse_any(input: ParseStream) -> Result { + input.step(|cursor| match cursor.ident() { + Some((ident, rest)) => Ok((ident, rest)), + None => Err(cursor.error("expected ident")), + }) + } + + fn unraw(&self) -> Ident { + let string = self.to_string(); + if let Some(string) = string.strip_prefix("r#") { + Ident::new(string, self.span()) + } else { + self.clone() + } + } +} + +impl Peek for private::PeekFn { + type Token = private::IdentAny; +} + +impl CustomToken for private::IdentAny { + fn peek(cursor: Cursor) -> bool { + cursor.ident().is_some() + } + + fn display() -> &'static str { + "identifier" + } +} + +impl lookahead::Sealed for private::PeekFn {} + +mod private { + use proc_macro2::Ident; + + pub trait Sealed {} + + impl Sealed for Ident {} + + pub struct PeekFn; + pub struct IdentAny; + + impl Copy for PeekFn {} + impl Clone for PeekFn { + fn clone(&self) -> Self { + *self + } + } +} -- cgit v1.3.1