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, 112 insertions, 0 deletions

diff --git a/sound/Kconfig b/sound/Kconfig
new file mode 100644
index 000000000..8b4020539
--- /dev/null
+++ b/sound/Kconfig
@@ -0,0 +1,112 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig SOUND
+	tristate "Sound card support"
+	depends on HAS_IOMEM || INDIRECT_IOMEM
+	help
+	  If you have a sound card in your computer, i.e. if it can say more
+	  than an occasional beep, say Y.
+
+if SOUND
+
+config SOUND_OSS_CORE
+	bool
+	default n
+
+config SOUND_OSS_CORE_PRECLAIM
+	bool "Preclaim OSS device numbers"
+	depends on SOUND_OSS_CORE
+	default y
+	help
+	  With this option enabled, the kernel will claim all OSS device
+	  numbers if any OSS support (native or emulation) is enabled
+	  whether the respective module is loaded or not and try to load the
+	  appropriate module using sound-slot/service-* and char-major-*
+	  module aliases when one of the device numbers is opened.  With
+	  this option disabled, kernel will only claim actually in-use
+	  device numbers and opening a missing device will generate only the
+	  standard char-major-* aliases.
+
+	  The only visible difference is use of additional module aliases
+	  and whether OSS sound devices appear multiple times in
+	  /proc/devices.  sound-slot/service-* module aliases are scheduled
+	  to be removed (ie. PRECLAIM won't be available) and this option is
+	  to make the transition easier.  This option can be overridden
+	  during boot using the kernel parameter soundcore.preclaim_oss.
+
+	  Disabling this allows alternative OSS implementations.
+
+	  If unsure, say Y.
+
+source "sound/oss/dmasound/Kconfig"
+
+menuconfig SND
+	tristate "Advanced Linux Sound Architecture"
+	help
+	  Say 'Y' or 'M' to enable ALSA (Advanced Linux Sound Architecture),
+	  the new base sound system.
+
+	  For more information, see <http://www.alsa-project.org/>
+
+if SND
+
+source "sound/core/Kconfig"
+
+source "sound/drivers/Kconfig"
+
+source "sound/isa/Kconfig"
+
+source "sound/pci/Kconfig"
+
+source "sound/hda/Kconfig"
+
+source "sound/ppc/Kconfig"
+
+source "sound/ac97/Kconfig"
+
+source "sound/aoa/Kconfig"
+
+source "sound/arm/Kconfig"
+
+source "sound/atmel/Kconfig"
+
+source "sound/spi/Kconfig"
+
+source "sound/mips/Kconfig"
+
+source "sound/sh/Kconfig"
+
+# the following will depend on the order of config.
+# here assuming USB is defined before ALSA
+source "sound/usb/Kconfig"
+
+source "sound/firewire/Kconfig"
+
+# the following will depend on the order of config.
+# here assuming PCMCIA is defined before ALSA
+source "sound/pcmcia/Kconfig"
+
+source "sound/sparc/Kconfig"
+
+source "sound/parisc/Kconfig"
+
+source "sound/soc/Kconfig"
+
+source "sound/x86/Kconfig"
+
+source "sound/synth/Kconfig"
+
+source "sound/xen/Kconfig"
+
+source "sound/virtio/Kconfig"
+
+endif # SND
+
+endif # SOUND
+
+config AC97_BUS
+	tristate
+	help
+	  This is used to avoid config and link hard dependencies between the
+	  sound subsystem and other function drivers completely unrelated to
+	  sound although they're sharing the AC97 bus. Concerned drivers
+	  should "select" this.