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 --- scripts/module.lds.S | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 scripts/module.lds.S (limited to 'scripts/module.lds.S') diff --git a/scripts/module.lds.S b/scripts/module.lds.S new file mode 100644 index 000000000..d0f200428 --- /dev/null +++ b/scripts/module.lds.S @@ -0,0 +1,63 @@ +/* + * Common module linker script, always used when linking a module. + * Archs are free to supply their own linker scripts. ld will + * combine them automatically. + */ + +#include + +SECTIONS { + /DISCARD/ : { + *(.discard) + *(.discard.*) + *(.export_symbol) + *(.no_trim_symbol) + } + + __ksymtab 0 : ALIGN(8) { *(SORT(___ksymtab+*)) } + __kcrctab 0 : ALIGN(4) { *(SORT(___kcrctab+*)) } + __kflagstab 0 : ALIGN(1) { *(SORT(___kflagstab+*)) } + + .ctors 0 : ALIGN(8) { *(SORT(.ctors.*)) *(.ctors) } + .init_array 0 : ALIGN(8) { *(SORT(.init_array.*)) *(.init_array) } + + .altinstructions 0 : ALIGN(8) { KEEP(*(.altinstructions)) } + __bug_table 0 : ALIGN(8) { KEEP(*(__bug_table)) } + __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) } + __ex_table 0 : ALIGN(4) { KEEP(*(__ex_table)) } + + __patchable_function_entries 0 : { *(__patchable_function_entries) } + + .init.klp_funcs 0 : ALIGN(8) { KEEP(*(.init.klp_funcs)) } + .init.klp_objects 0 : ALIGN(8) { KEEP(*(.init.klp_objects)) } + +#ifdef CONFIG_ARCH_USES_CFI_TRAPS + __kcfi_traps 0 : { KEEP(*(.kcfi_traps)) } +#endif + +#ifndef CONFIG_ARCH_WANTS_MODULES_TEXT_SECTIONS + .text 0 : { + *(.text .text.[0-9a-zA-Z_]*) + } +#endif + + .bss 0 : { + *(.bss .bss.[0-9a-zA-Z_]*) + *(.bss..L*) + } + + .data 0 : { + *(.data .data.[0-9a-zA-Z_]*) + *(.data..L*) + } + + .rodata 0 : { + *(.rodata .rodata.[0-9a-zA-Z_]*) + *(.rodata..L*) + } + + MOD_SEPARATE_CODETAG_SECTIONS() +} + +/* bring in arch-specific sections */ +#include -- cgit v1.3.1