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 --- drivers/char/Makefile | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 drivers/char/Makefile (limited to 'drivers/char/Makefile') diff --git a/drivers/char/Makefile b/drivers/char/Makefile new file mode 100644 index 000000000..a46d7bf7c --- /dev/null +++ b/drivers/char/Makefile @@ -0,0 +1,43 @@ +# SPDX-License-Identifier: GPL-2.0 +# +# Makefile for the kernel character device drivers. +# + +obj-y += mem.o random.o +obj-$(CONFIG_TTY_PRINTK) += ttyprintk.o +obj-y += misc.o +obj-$(CONFIG_TEST_MISC_MINOR) += misc_minor_kunit.o +obj-$(CONFIG_ATARI_DSP56K) += dsp56k.o +obj-$(CONFIG_VIRTIO_CONSOLE) += virtio_console.o +obj-$(CONFIG_UV_MMTIMER) += uv_mmtimer.o +obj-$(CONFIG_IBM_BSR) += bsr.o + +obj-$(CONFIG_PRINTER) += lp.o + +obj-$(CONFIG_APM_EMULATION) += apm-emulation.o + +obj-$(CONFIG_SONYPI) += sonypi.o +obj-$(CONFIG_HPET) += hpet.o +obj-$(CONFIG_XILINX_HWICAP) += xilinx_hwicap/ +obj-$(CONFIG_NVRAM) += nvram.o +obj-$(CONFIG_TOSHIBA) += toshiba.o +obj-$(CONFIG_DS1620) += ds1620.o +obj-$(CONFIG_HW_RANDOM) += hw_random/ +obj-$(CONFIG_PPDEV) += ppdev.o +obj-$(CONFIG_NWBUTTON) += nwbutton.o +obj-$(CONFIG_NWFLASH) += nwflash.o +obj-$(CONFIG_SCx200_GPIO) += scx200_gpio.o +obj-$(CONFIG_PC8736x_GPIO) += pc8736x_gpio.o +obj-$(CONFIG_NSC_GPIO) += nsc_gpio.o +obj-$(CONFIG_TELCLOCK) += tlclk.o + +obj-y += agp/ + +obj-$(CONFIG_HANGCHECK_TIMER) += hangcheck-timer.o +obj-$(CONFIG_TCG_TPM) += tpm/ + +obj-$(CONFIG_PS3_FLASH) += ps3flash.o + +obj-$(CONFIG_XILLYBUS_CLASS) += xillybus/ +obj-$(CONFIG_POWERNV_OP_PANEL) += powernv-op-panel.o +obj-$(CONFIG_ADI) += adi.o -- cgit v1.3.1