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 --- mm/interval_tree.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 mm/interval_tree.c (limited to 'mm/interval_tree.c') diff --git a/mm/interval_tree.c b/mm/interval_tree.c new file mode 100644 index 000000000..7bbbf15cf --- /dev/null +++ b/mm/interval_tree.c @@ -0,0 +1,135 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * mm/interval_tree.c - interval tree for address_space->i_mmap and + * anon_vma->rb_root + * + * Copyright (C) 2012, Michel Lespinasse + */ + +#include +#include +#include +#include + +/* File-backed interval tree (address_space->i_mmap) */ + +INTERVAL_TREE_DEFINE(struct vm_area_struct, shared.rb, + pgoff_t, shared.rb_subtree_last, + vma_start_pgoff, vma_last_pgoff, static, + __mapping_rmap_tree) + +void mapping_rmap_tree_insert(struct vm_area_struct *vma, + struct address_space *mapping) +{ + __mapping_rmap_tree_insert(vma, &mapping->i_mmap); +} + +/* Insert vma immediately after prev in the interval tree */ +void mapping_rmap_tree_insert_after(struct vm_area_struct *vma, + struct vm_area_struct *prev, + struct address_space *mapping) +{ + struct rb_node **link; + struct vm_area_struct *parent; + const pgoff_t pgoff_last = vma_last_pgoff(vma); + + VM_WARN_ON_ONCE_VMA(vma_start_pgoff(vma) != vma_start_pgoff(prev), vma); + + if (!prev->shared.rb.rb_right) { + parent = prev; + link = &prev->shared.rb.rb_right; + } else { + parent = rb_entry(prev->shared.rb.rb_right, + struct vm_area_struct, shared.rb); + if (parent->shared.rb_subtree_last < pgoff_last) + parent->shared.rb_subtree_last = pgoff_last; + while (parent->shared.rb.rb_left) { + parent = rb_entry(parent->shared.rb.rb_left, + struct vm_area_struct, shared.rb); + if (parent->shared.rb_subtree_last < pgoff_last) + parent->shared.rb_subtree_last = pgoff_last; + } + link = &parent->shared.rb.rb_left; + } + + vma->shared.rb_subtree_last = pgoff_last; + rb_link_node(&vma->shared.rb, &parent->shared.rb, link); + rb_insert_augmented(&vma->shared.rb, &mapping->i_mmap.rb_root, + &__mapping_rmap_tree_augment); +} + +void mapping_rmap_tree_remove(struct vm_area_struct *vma, + struct address_space *mapping) +{ + __mapping_rmap_tree_remove(vma, &mapping->i_mmap); +} + +struct vm_area_struct * +mapping_rmap_tree_iter_first(struct address_space *mapping, + pgoff_t pgoff_start, pgoff_t pgoff_last) +{ + return __mapping_rmap_tree_iter_first(&mapping->i_mmap, + pgoff_start, pgoff_last); +} + +struct vm_area_struct * +mapping_rmap_tree_iter_next(struct vm_area_struct *vma, + pgoff_t pgoff_start, pgoff_t pgoff_last) +{ + return __mapping_rmap_tree_iter_next(vma, pgoff_start, pgoff_last); +} + +/* Anonymous interval tree (anon_vma->rb_root) */ + +static pgoff_t avc_start_pgoff(struct anon_vma_chain *avc) +{ + return vma_start_anon_pgoff(avc->vma); +} + +static pgoff_t avc_last_pgoff(struct anon_vma_chain *avc) +{ + return vma_last_anon_pgoff(avc->vma); +} + +INTERVAL_TREE_DEFINE(struct anon_vma_chain, rb, pgoff_t, rb_subtree_last, + avc_start_pgoff, avc_last_pgoff, + static, __anon_rmap_tree) + +void anon_rmap_tree_insert(struct anon_vma_chain *avc, + struct anon_vma *anon_vma) +{ +#ifdef CONFIG_DEBUG_VM_RB + avc->cached_vma_start = avc_start_pgoff(avc); + avc->cached_vma_last = avc_last_pgoff(avc); +#endif + __anon_rmap_tree_insert(avc, &anon_vma->rb_root); +} + +void anon_rmap_tree_remove(struct anon_vma_chain *avc, + struct anon_vma *anon_vma) +{ + __anon_rmap_tree_remove(avc, &anon_vma->rb_root); +} + +struct anon_vma_chain * +anon_rmap_tree_iter_first(struct anon_vma *anon_vma, + pgoff_t pgoff_start, pgoff_t pgoff_last) +{ + return __anon_rmap_tree_iter_first(&anon_vma->rb_root, + pgoff_start, pgoff_last); +} + +struct anon_vma_chain * +anon_rmap_tree_iter_next(struct anon_vma_chain *avc, + pgoff_t pgoff_start, pgoff_t pgoff_last) +{ + return __anon_rmap_tree_iter_next(avc, pgoff_start, pgoff_last); +} + +#ifdef CONFIG_DEBUG_VM_RB +void anon_rmap_tree_verify(struct anon_vma_chain *avc) +{ + WARN_ON_ONCE(avc->cached_vma_start != avc_start_pgoff(avc)); + WARN_ON_ONCE(avc->cached_vma_last != avc_last_pgoff(avc)); +} +#endif -- cgit v1.3.1