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 --- io_uring/cancel.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 io_uring/cancel.h (limited to 'io_uring/cancel.h') diff --git a/io_uring/cancel.h b/io_uring/cancel.h new file mode 100644 index 000000000..1b201a094 --- /dev/null +++ b/io_uring/cancel.h @@ -0,0 +1,49 @@ +// SPDX-License-Identifier: GPL-2.0 +#ifndef IORING_CANCEL_H +#define IORING_CANCEL_H + +#include + +struct io_cancel_data { + struct io_ring_ctx *ctx; + u64 data; + struct file *file; + u8 opcode; + u32 flags; + int seq; +}; + +int io_async_cancel_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe); +int io_async_cancel(struct io_kiocb *req, unsigned int issue_flags); + +int io_try_cancel(struct io_uring_task *tctx, struct io_cancel_data *cd, + unsigned int issue_flags); + +int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg); +bool io_cancel_req_match(struct io_kiocb *req, struct io_cancel_data *cd); +bool io_match_task_safe(struct io_kiocb *head, struct io_uring_task *tctx, + bool cancel_all); + +bool io_cancel_remove_all(struct io_ring_ctx *ctx, struct io_uring_task *tctx, + struct hlist_head *list, bool cancel_all, + bool (*cancel)(struct io_kiocb *)); +int io_cancel_remove(struct io_ring_ctx *ctx, struct io_cancel_data *cd, + unsigned int issue_flags, struct hlist_head *list, + bool (*cancel)(struct io_kiocb *)); +__cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx, + struct io_uring_task *tctx, + bool cancel_all, bool is_sqpoll_thread); +__cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd); +__cold bool io_cancel_ctx_cb(struct io_wq_work *work, void *data); + +static inline bool io_cancel_match_sequence(struct io_kiocb *req, int sequence) +{ + if (req->cancel_seq_set && sequence == req->work.cancel_seq) + return true; + + req->cancel_seq_set = true; + req->work.cancel_seq = sequence; + return false; +} + +#endif -- cgit v1.3.1