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 --- include/asm-generic/cacheflush.h | 127 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 include/asm-generic/cacheflush.h (limited to 'include/asm-generic/cacheflush.h') diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h new file mode 100644 index 000000000..7ee8a179d --- /dev/null +++ b/include/asm-generic/cacheflush.h @@ -0,0 +1,127 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_GENERIC_CACHEFLUSH_H +#define _ASM_GENERIC_CACHEFLUSH_H + +#include + +struct mm_struct; +struct vm_area_struct; +struct page; +struct address_space; + +/* + * The cache doesn't need to be flushed when TLB entries change when + * the cache is mapped to physical memory, not virtual memory + */ +#ifndef flush_cache_all +static inline void flush_cache_all(void) +{ +} +#endif + +#ifndef flush_cache_mm +static inline void flush_cache_mm(struct mm_struct *mm) +{ +} +#endif + +#ifndef flush_cache_dup_mm +static inline void flush_cache_dup_mm(struct mm_struct *mm) +{ +} +#endif + +#ifndef flush_cache_range +static inline void flush_cache_range(struct vm_area_struct *vma, + unsigned long start, + unsigned long end) +{ +} +#endif + +#ifndef flush_cache_page +static inline void flush_cache_page(struct vm_area_struct *vma, + unsigned long vmaddr, + unsigned long pfn) +{ +} +#endif + +#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE +static inline void flush_dcache_page(struct page *page) +{ +} + +#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0 +#endif + +#ifndef flush_dcache_mmap_lock +static inline void flush_dcache_mmap_lock(struct address_space *mapping) +{ +} +#endif + +#ifndef flush_dcache_mmap_unlock +static inline void flush_dcache_mmap_unlock(struct address_space *mapping) +{ +} +#endif + +#ifndef flush_icache_range +static inline void flush_icache_range(unsigned long start, unsigned long end) +{ +} +#endif + +#ifndef flush_icache_user_range +#define flush_icache_user_range flush_icache_range +#endif + +#ifndef flush_icache_user_page +static inline void flush_icache_user_page(struct vm_area_struct *vma, + struct page *page, + unsigned long addr, int len) +{ +} +#endif + +#ifndef flush_cache_vmap +static inline void flush_cache_vmap(unsigned long start, unsigned long end) +{ +} +#endif + +#ifndef flush_cache_vmap_early +static inline void flush_cache_vmap_early(unsigned long start, unsigned long end) +{ +} +#endif + +#ifndef flush_cache_vunmap +static inline void flush_cache_vunmap(unsigned long start, unsigned long end) +{ +} +#endif + +#ifndef copy_to_user_page +#define copy_to_user_page(vma, page, vaddr, dst, src, len) \ + do { \ + instrument_copy_to_user((void __user *)dst, src, len); \ + memcpy(dst, src, len); \ + flush_icache_user_page(vma, page, vaddr, len); \ + } while (0) +#endif + + +#ifndef copy_from_user_page +#define copy_from_user_page(vma, page, vaddr, dst, src, len) \ + do { \ + instrument_copy_from_user_before(dst, (void __user *)src, \ + len); \ + memcpy(dst, src, len); \ + instrument_copy_from_user_after(dst, (void __user *)src, len, \ + 0); \ + } while (0) +#endif + +#endif /* _ASM_GENERIC_CACHEFLUSH_H */ -- cgit v1.3.1