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/getuser.S | 167 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 167 insertions(+) create mode 100644 arch/arm/lib/getuser.S (limited to 'arch/arm/lib/getuser.S') diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S new file mode 100644 index 000000000..c5e420750 --- /dev/null +++ b/arch/arm/lib/getuser.S @@ -0,0 +1,167 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * linux/arch/arm/lib/getuser.S + * + * Copyright (C) 2001 Russell King + * + * Idea from x86 version, (C) Copyright 1998 Linus Torvalds + * + * These functions have a non-standard call interface to make them more + * efficient, especially as they return an error value in addition to + * the "real" return value. + * + * __get_user_X + * + * Inputs: r0 contains the address + * r1 contains the address limit, which must be preserved + * Outputs: r0 is the error code + * r2, r3 contains the zero-extended value + * lr corrupted + * + * No other registers must be altered. (see + * for specific ASM register usage). + * + * Note that ADDR_LIMIT is either 0 or 0xc0000000. + * Note also that it is intended that __get_user_bad is not global. + */ +#include +#include +#include +#include + +ENTRY(__get_user_1) + check_uaccess r0, 1, r1, r2, __get_user_bad +1: TUSER(ldrb) r2, [r0] + mov r0, #0 + ret lr +ENDPROC(__get_user_1) +_ASM_NOKPROBE(__get_user_1) + +ENTRY(__get_user_2) + check_uaccess r0, 2, r1, r2, __get_user_bad +#if __LINUX_ARM_ARCH__ >= 6 + +2: TUSER(ldrh) r2, [r0] + +#else + +#ifdef CONFIG_CPU_USE_DOMAINS +rb .req ip +2: ldrbt r2, [r0], #1 +3: ldrbt rb, [r0], #0 +#else +rb .req r0 +2: ldrb r2, [r0] +3: ldrb rb, [r0, #1] +#endif +#ifndef __ARMEB__ + orr r2, r2, rb, lsl #8 +#else + orr r2, rb, r2, lsl #8 +#endif + +#endif /* __LINUX_ARM_ARCH__ >= 6 */ + + mov r0, #0 + ret lr +ENDPROC(__get_user_2) +_ASM_NOKPROBE(__get_user_2) + +ENTRY(__get_user_4) + check_uaccess r0, 4, r1, r2, __get_user_bad +4: TUSER(ldr) r2, [r0] + mov r0, #0 + ret lr +ENDPROC(__get_user_4) +_ASM_NOKPROBE(__get_user_4) + +ENTRY(__get_user_8) + check_uaccess r0, 8, r1, r2, __get_user_bad8 +#ifdef CONFIG_THUMB2_KERNEL +5: TUSER(ldr) r2, [r0] +6: TUSER(ldr) r3, [r0, #4] +#else +5: TUSER(ldr) r2, [r0], #4 +6: TUSER(ldr) r3, [r0] +#endif + mov r0, #0 + ret lr +ENDPROC(__get_user_8) +_ASM_NOKPROBE(__get_user_8) + +#ifdef __ARMEB__ +ENTRY(__get_user_32t_8) + check_uaccess r0, 8, r1, r2, __get_user_bad +#ifdef CONFIG_CPU_USE_DOMAINS + add r0, r0, #4 +7: ldrt r2, [r0] +#else +7: ldr r2, [r0, #4] +#endif + mov r0, #0 + ret lr +ENDPROC(__get_user_32t_8) +_ASM_NOKPROBE(__get_user_32t_8) + +ENTRY(__get_user_64t_1) + check_uaccess r0, 1, r1, r2, __get_user_bad8 +8: TUSER(ldrb) r3, [r0] + mov r0, #0 + ret lr +ENDPROC(__get_user_64t_1) +_ASM_NOKPROBE(__get_user_64t_1) + +ENTRY(__get_user_64t_2) + check_uaccess r0, 2, r1, r2, __get_user_bad8 +#ifdef CONFIG_CPU_USE_DOMAINS +rb .req ip +9: ldrbt r3, [r0], #1 +10: ldrbt rb, [r0], #0 +#else +rb .req r0 +9: ldrb r3, [r0] +10: ldrb rb, [r0, #1] +#endif + orr r3, rb, r3, lsl #8 + mov r0, #0 + ret lr +ENDPROC(__get_user_64t_2) +_ASM_NOKPROBE(__get_user_64t_2) + +ENTRY(__get_user_64t_4) + check_uaccess r0, 4, r1, r2, __get_user_bad8 +11: TUSER(ldr) r3, [r0] + mov r0, #0 + ret lr +ENDPROC(__get_user_64t_4) +_ASM_NOKPROBE(__get_user_64t_4) +#endif + +__get_user_bad8: + mov r3, #0 +__get_user_bad: + mov r2, #0 + mov r0, #-EFAULT + ret lr +ENDPROC(__get_user_bad) +ENDPROC(__get_user_bad8) +_ASM_NOKPROBE(__get_user_bad) +_ASM_NOKPROBE(__get_user_bad8) + +.pushsection __ex_table, "a" + .long 1b, __get_user_bad + .long 2b, __get_user_bad +#if __LINUX_ARM_ARCH__ < 6 + .long 3b, __get_user_bad +#endif + .long 4b, __get_user_bad + .long 5b, __get_user_bad8 + .long 6b, __get_user_bad8 +#ifdef __ARMEB__ + .long 7b, __get_user_bad + .long 8b, __get_user_bad8 + .long 9b, __get_user_bad8 + .long 10b, __get_user_bad8 + .long 11b, __get_user_bad8 +#endif +.popsection -- cgit v1.3.1