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/memmap.h | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 io_uring/memmap.h (limited to 'io_uring/memmap.h') diff --git a/io_uring/memmap.h b/io_uring/memmap.h new file mode 100644 index 000000000..f4cfbb6b9 --- /dev/null +++ b/io_uring/memmap.h @@ -0,0 +1,52 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef IO_URING_MEMMAP_H +#define IO_URING_MEMMAP_H + +#define IORING_MAP_OFF_PARAM_REGION 0x20000000ULL +#define IORING_MAP_OFF_ZCRX_REGION 0x30000000ULL + +#define IORING_OFF_ZCRX_SHIFT 16 + +struct page **io_pin_pages(unsigned long uaddr, unsigned long len, int *npages); + +#ifndef CONFIG_MMU +unsigned int io_uring_nommu_mmap_capabilities(struct file *file); +#endif +unsigned long io_uring_get_unmapped_area(struct file *file, unsigned long addr, + unsigned long len, unsigned long pgoff, + unsigned long flags); +int io_uring_mmap(struct file *file, struct vm_area_struct *vma); + +void io_free_region(struct user_struct *user, struct io_mapped_region *mr); +int io_create_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr, + struct io_uring_region_desc *reg, + unsigned long mmap_offset); + +static inline void *io_region_get_ptr(struct io_mapped_region *mr) +{ + return mr->ptr; +} + +static inline bool io_region_is_set(struct io_mapped_region *mr) +{ + return !!mr->nr_pages; +} + +static inline void io_region_publish(struct io_ring_ctx *ctx, + struct io_mapped_region *src_region, + struct io_mapped_region *dst_region) +{ + /* + * Once published mmap can find it without holding only the ->mmap_lock + * and not ->uring_lock. + */ + guard(mutex)(&ctx->mmap_lock); + *dst_region = *src_region; +} + +static inline size_t io_region_size(struct io_mapped_region *mr) +{ + return (size_t) mr->nr_pages << PAGE_SHIFT; +} + +#endif -- cgit v1.3.1