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/x86/lib/getuser.S | 172 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 172 insertions(+) create mode 100644 arch/x86/lib/getuser.S (limited to 'arch/x86/lib/getuser.S') diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S new file mode 100644 index 000000000..9d5654b8a --- /dev/null +++ b/arch/x86/lib/getuser.S @@ -0,0 +1,172 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * __get_user functions. + * + * (C) Copyright 1998 Linus Torvalds + * (C) Copyright 2005 Andi Kleen + * (C) Copyright 2008 Glauber Costa + * + * 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: %[r|e]ax contains the address. + * + * Outputs: %[r|e]ax is error code (0 or -EFAULT) + * %[r|e]dx contains zero-extended value + * %ecx contains the high half for 32-bit __get_user_8 + * + * + * These functions should not modify any other registers, + * as they get called from within inline assembly. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC + +.macro check_range size:req +.if IS_ENABLED(CONFIG_X86_64) + RUNTIME_CONST_PTR USER_PTR_MAX, rdx + cmp %rdx, %rax + cmova %rdx, %rax +.else + cmp $TASK_SIZE_MAX-\size+1, %eax + jae .Lbad_get_user + sbb %edx, %edx /* array_index_mask_nospec() */ + and %edx, %eax +.endif +.endm + +.macro UACCESS op src dst +1: \op \src,\dst + _ASM_EXTABLE_UA(1b, __get_user_handle_exception) +.endm + + + .text +SYM_FUNC_START(__get_user_1) + ANNOTATE_NOENDBR + check_range size=1 + ASM_STAC + UACCESS movzbl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_1) +EXPORT_SYMBOL(__get_user_1) + +SYM_FUNC_START(__get_user_2) + ANNOTATE_NOENDBR + check_range size=2 + ASM_STAC + UACCESS movzwl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_2) +EXPORT_SYMBOL(__get_user_2) + +SYM_FUNC_START(__get_user_4) + ANNOTATE_NOENDBR + check_range size=4 + ASM_STAC + UACCESS movl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_4) +EXPORT_SYMBOL(__get_user_4) + +SYM_FUNC_START(__get_user_8) + ANNOTATE_NOENDBR +#ifndef CONFIG_X86_64 + xor %ecx,%ecx +#endif + check_range size=8 + ASM_STAC +#ifdef CONFIG_X86_64 + UACCESS movq (%_ASM_AX),%rdx +#else + UACCESS movl (%_ASM_AX),%edx + UACCESS movl 4(%_ASM_AX),%ecx +#endif + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_8) +EXPORT_SYMBOL(__get_user_8) + +/* .. and the same for __get_user, just without the range checks */ +SYM_FUNC_START(__get_user_nocheck_1) + ANNOTATE_NOENDBR + ASM_STAC + ASM_BARRIER_NOSPEC + UACCESS movzbl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_nocheck_1) +EXPORT_SYMBOL(__get_user_nocheck_1) + +SYM_FUNC_START(__get_user_nocheck_2) + ANNOTATE_NOENDBR + ASM_STAC + ASM_BARRIER_NOSPEC + UACCESS movzwl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_nocheck_2) +EXPORT_SYMBOL(__get_user_nocheck_2) + +SYM_FUNC_START(__get_user_nocheck_4) + ANNOTATE_NOENDBR + ASM_STAC + ASM_BARRIER_NOSPEC + UACCESS movl (%_ASM_AX),%edx + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_nocheck_4) +EXPORT_SYMBOL(__get_user_nocheck_4) + +SYM_FUNC_START(__get_user_nocheck_8) + ANNOTATE_NOENDBR + ASM_STAC + ASM_BARRIER_NOSPEC +#ifdef CONFIG_X86_64 + UACCESS movq (%_ASM_AX),%rdx +#else + xor %ecx,%ecx + UACCESS movl (%_ASM_AX),%edx + UACCESS movl 4(%_ASM_AX),%ecx +#endif + xor %eax,%eax + ASM_CLAC + RET +SYM_FUNC_END(__get_user_nocheck_8) +EXPORT_SYMBOL(__get_user_nocheck_8) + + +SYM_CODE_START_LOCAL(__get_user_handle_exception) + ASM_CLAC +.Lbad_get_user: + xor %edx,%edx + mov $(-EFAULT),%_ASM_AX + RET +SYM_CODE_END(__get_user_handle_exception) -- cgit v1.3.1