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, 61 insertions, 0 deletions

diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
new file mode 100644
index 000000000..dd93ae8a6
--- /dev/null
+++ b/mm/kasan/Makefile
@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: GPL-2.0
+KASAN_SANITIZE := n
+UBSAN_SANITIZE := n
+KCOV_INSTRUMENT := n
+
+# Disable ftrace to avoid recursion.
+CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_generic.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_init.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_quarantine.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report_generic.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report_hw_tags.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_report_sw_tags.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_shadow.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_hw_tags.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_sw_tags.o = $(CC_FLAGS_FTRACE)
+
+# Function splitter causes unnecessary splits in __asan_load1/__asan_store1
+# see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
+CC_FLAGS_KASAN_RUNTIME := $(call cc-option, -fno-conserve-stack)
+CC_FLAGS_KASAN_RUNTIME += -fno-stack-protector
+# Disable branch tracing to avoid recursion.
+CC_FLAGS_KASAN_RUNTIME += -DDISABLE_BRANCH_PROFILING
+
+CFLAGS_common.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_generic.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_init.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_quarantine.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_report.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_report_generic.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_report_hw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_report_sw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_shadow.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_hw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
+CFLAGS_sw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
+
+CFLAGS_KASAN_TEST := $(CFLAGS_KASAN)
+ifndef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+# If compiler instruments memintrinsics by prefixing them with __asan/__hwasan,
+# we need to treat them normally (as builtins), otherwise the compiler won't
+# recognize them as instrumentable. If it doesn't instrument them, we need to
+# pass -fno-builtin, so the compiler doesn't inline them.
+CFLAGS_KASAN_TEST += -fno-builtin
+endif
+
+CFLAGS_REMOVE_kasan_test_c.o += $(call cc-option, -Wvla-larger-than=1)
+CFLAGS_kasan_test_c.o := $(CFLAGS_KASAN_TEST)
+RUSTFLAGS_kasan_test_rust.o := $(RUSTFLAGS_KASAN)
+
+obj-y := common.o report.o
+obj-$(CONFIG_KASAN_GENERIC) += init.o generic.o report_generic.o shadow.o quarantine.o
+obj-$(CONFIG_KASAN_HW_TAGS) += hw_tags.o report_hw_tags.o tags.o report_tags.o
+obj-$(CONFIG_KASAN_SW_TAGS) += init.o report_sw_tags.o shadow.o sw_tags.o tags.o report_tags.o
+
+kasan_test-objs := kasan_test_c.o
+ifdef CONFIG_RUST
+	kasan_test-objs += kasan_test_rust.o
+endif
+
+obj-$(CONFIG_KASAN_KUNIT_TEST) += kasan_test.o