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 --- arch/arm/lib/Makefile | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 arch/arm/lib/Makefile (limited to 'arch/arm/lib/Makefile') diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile new file mode 100644 index 000000000..9295055cd --- /dev/null +++ b/arch/arm/lib/Makefile @@ -0,0 +1,42 @@ +# SPDX-License-Identifier: GPL-2.0 +# +# linux/arch/arm/lib/Makefile +# +# Copyright (C) 1995-2000 Russell King +# + +lib-y := changebit.o csumipv6.o csumpartial.o \ + csumpartialcopy.o csumpartialcopyuser.o clearbit.o \ + delay.o delay-loop.o findbit.o memchr.o memcpy.o \ + memmove.o memset.o setbit.o \ + strchr.o strrchr.o \ + testchangebit.o testclearbit.o testsetbit.o \ + ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \ + ucmpdi2.o lib1funcs.o div64.o \ + io-readsb.o io-writesb.o io-readsl.o io-writesl.o \ + call_with_stack.o bswapsdi2.o + +mmu-y := clear_user.o copy_page.o getuser.o putuser.o \ + copy_from_user.o copy_to_user.o + +ifdef CONFIG_CC_IS_CLANG + lib-y += backtrace-clang.o +else + lib-y += backtrace.o +endif + +# using lib_ here won't override already available weak symbols +obj-$(CONFIG_UACCESS_WITH_MEMCPY) += uaccess_with_memcpy.o + +lib-$(CONFIG_MMU) += $(mmu-y) + +ifeq ($(CONFIG_CPU_32v3),y) + lib-y += io-readsw-armv3.o io-writesw-armv3.o +else + lib-y += io-readsw-armv4.o io-writesw-armv4.o +endif + +$(obj)/csumpartialcopy.o: $(obj)/csumpartialcopygeneric.S +$(obj)/csumpartialcopyuser.o: $(obj)/csumpartialcopygeneric.S + +obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o -- cgit v1.3.1