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 --- scripts/rustdoc_test_builder.rs | 78 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 scripts/rustdoc_test_builder.rs (limited to 'scripts/rustdoc_test_builder.rs') diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs new file mode 100644 index 000000000..df864437c --- /dev/null +++ b/scripts/rustdoc_test_builder.rs @@ -0,0 +1,78 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Test builder for `rustdoc`-generated tests. +//! +//! This script is a hack to extract the test from `rustdoc`'s output. Ideally, `rustdoc` would +//! have an option to generate this information instead, e.g. as JSON output. +//! +//! The `rustdoc`-generated test names look like `{file}_{line}_{number}`, e.g. +//! `...path_rust_kernel_sync_arc_rs_42_0`. `number` is the "test number", needed in cases like +//! a macro that expands into items with doctests is invoked several times within the same line. +//! +//! However, since these names are used for bisection in CI, the line number makes it not stable +//! at all. In the future, we would like `rustdoc` to give us the Rust item path associated with +//! the test, plus a "test number" (for cases with several examples per item) and generate a name +//! from that. For the moment, we generate ourselves a new name, `{file}_{number}` instead, in +//! the `gen` script (done there since we need to be aware of all the tests in a given file). + +use std::io::Read; + +fn main() { + let mut stdin = std::io::stdin().lock(); + let mut body = String::new(); + stdin.read_to_string(&mut body).unwrap(); + + // Find the generated function name looking for the inner function inside `main()`. + // + // The line we are looking for looks like one of the following: + // + // ``` + // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() { + // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> { + // ``` + // + // It should be unlikely that doctest code matches such lines (when code is formatted properly). + let rustdoc_function_name = body + .lines() + .find_map(|line| { + Some( + line.split_once("fn main() {")? + .1 + .split_once("fn ")? + .1 + .split_once("()")? + .0, + ) + .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_')) + }) + .expect("No test function found in `rustdoc`'s output."); + + // Replicate `rustdoc` 1.87+ behaviour [1] by fully qualifying `Result` to avoid the collision + // with our own `Result` coming from the prelude. + // + // [1]: https://github.com/rust-lang/rust/pull/137807 + // + // TODO: Remove this when MSRV is bumped above 1.87. + let body = body.replace( + &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"), + // This intentionally does not use absolute paths to match `rustdoc` 1.87 behaviour. + &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"), + ); + + // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on + // the return value to check there were no returned errors. Instead, we use our assert macro + // since we want to just fail the test, not panic the kernel. + // + // We save the result in a variable so that the failed assertion message looks nicer. + let body = body.replace( + &format!("}} {rustdoc_function_name}().unwrap() }}"), + &format!("}} let test_return_value = {rustdoc_function_name}(); assert!(test_return_value.is_ok()); }}"), + ); + + // Figure out a smaller test name based on the generated function name. + let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1; + + let path = format!("rust/test/doctests/kernel/{name}"); + + std::fs::write(path, body.as_bytes()).unwrap(); +} -- cgit v1.3.1