sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

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 <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 65 insertions, 0 deletions

diff --git a/drivers/net/wan/Makefile b/drivers/net/wan/Makefile
new file mode 100644
index 000000000..00e9b7ee1
--- /dev/null
+++ b/drivers/net/wan/Makefile
@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the Linux network (wan) device drivers.
+#
+# 3 Aug 2000, Christoph Hellwig <hch@infradead.org>
+# Rewritten to use lists instead of if-statements.
+#
+
+obj-$(CONFIG_HDLC)		+= hdlc.o
+obj-$(CONFIG_HDLC_RAW)		+= hdlc_raw.o
+obj-$(CONFIG_HDLC_RAW_ETH)	+= hdlc_raw_eth.o
+obj-$(CONFIG_HDLC_CISCO)	+= hdlc_cisco.o
+obj-$(CONFIG_HDLC_FR)		+= hdlc_fr.o
+obj-$(CONFIG_HDLC_PPP)		+= hdlc_ppp.o
+obj-$(CONFIG_HDLC_X25)		+= hdlc_x25.o
+
+obj-y				+= framer/
+
+obj-$(CONFIG_FARSYNC)		+= farsync.o
+
+obj-$(CONFIG_LAPBETHER)		+= lapbether.o
+obj-$(CONFIG_N2)		+= n2.o
+obj-$(CONFIG_C101)		+= c101.o
+obj-$(CONFIG_WANXL)		+= wanxl.o
+obj-$(CONFIG_PCI200SYN)		+= pci200syn.o
+obj-$(CONFIG_PC300TOO)		+= pc300too.o
+obj-$(CONFIG_IXP4XX_HSS)	+= ixp4xx_hss.o
+obj-$(CONFIG_FSL_QMC_HDLC)	+= fsl_qmc_hdlc.o
+obj-$(CONFIG_FSL_UCC_HDLC)	+= fsl_ucc_hdlc.o
+obj-$(CONFIG_SLIC_DS26522)	+= slic_ds26522.o
+
+clean-files := wanxlfw.inc
+$(obj)/wanxl.o:	$(obj)/wanxlfw.inc
+
+CROSS_COMPILE_M68K = m68k-linux-gnu-
+
+ifeq ($(CONFIG_WANXL_BUILD_FIRMWARE),y)
+ifeq ($(ARCH),m68k)
+  M68KCC = $(CC)
+  M68KLD = $(LD)
+else
+  M68KCC = $(CROSS_COMPILE_M68K)gcc
+  M68KLD = $(CROSS_COMPILE_M68K)ld
+endif
+
+quiet_cmd_build_wanxlfw = BLDFW   $@
+      cmd_build_wanxlfw = hexdump -ve '"\n" 16/1 "0x%02X,"' $< | \
+	sed 's/0x  ,//g;1s/^/static const u8 firmware[]={/;$$s/,$$/\n};\n/' > $@
+
+$(obj)/wanxlfw.inc: $(obj)/wanxlfw.bin FORCE
+	$(call if_changed,build_wanxlfw)
+
+quiet_cmd_m68kld_bin_o = M68KLD  $@
+      cmd_m68kld_bin_o = $(M68KLD) --oformat binary -Ttext 0x1000 $< -o $@
+
+$(obj)/wanxlfw.bin: $(obj)/wanxlfw.o FORCE
+	$(call if_changed,m68kld_bin_o)
+
+quiet_cmd_m68kas_o_S = M68KAS  $@
+      cmd_m68kas_o_S = $(M68KCC) -D__ASSEMBLY__ -Wp,-MD,$(depfile) -I$(srctree)/include/uapi -c -o $@ $<
+
+$(obj)/wanxlfw.o: $(src)/wanxlfw.S FORCE
+	$(call if_changed_dep,m68kas_o_S)
+endif
+targets += wanxlfw.inc wanxlfw.bin wanxlfw.o