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, 77 insertions, 0 deletions

diff --git a/drivers/usb/usbip/Kconfig b/drivers/usb/usbip/Kconfig
new file mode 100644
index 000000000..50945b6fa
--- /dev/null
+++ b/drivers/usb/usbip/Kconfig
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config USBIP_CORE
+	tristate "USB/IP support"
+	depends on NET
+	select USB_COMMON
+	select SGL_ALLOC
+	help
+	  This enables pushing USB packets over IP to allow remote
+	  machines direct access to USB devices. It provides the
+	  USB/IP core that is required by both drivers.
+
+	  For more details, and to get the userspace utility
+	  programs, please see <http://usbip.sourceforge.net/>.
+
+	  To compile this as a module, choose M here: the module will
+	  be called usbip-core.
+
+	  If unsure, say N.
+
+config USBIP_VHCI_HCD
+	tristate "VHCI hcd"
+	depends on USBIP_CORE && USB
+	help
+	  This enables the USB/IP virtual host controller driver,
+	  which is run on the remote machine.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called vhci-hcd.
+
+config USBIP_VHCI_HC_PORTS
+	int "Number of ports per USB/IP virtual host controller"
+	range 1 15
+	default 8
+	depends on USBIP_VHCI_HCD
+	help
+	  To increase number of ports available for USB/IP virtual
+	  host controller driver, this defines number of ports per
+	  USB/IP virtual host controller.
+
+config USBIP_VHCI_NR_HCS
+	int "Number of USB/IP virtual host controllers"
+	range 1 32
+	default 1
+	depends on USBIP_VHCI_HCD
+	help
+	  To increase number of ports available for USB/IP virtual
+	  host controller driver, this defines number of USB/IP
+	  virtual host controllers as if adding physical host
+	  controllers.
+
+config USBIP_HOST
+	tristate "Host driver"
+	depends on USBIP_CORE && USB
+	help
+	  This enables the USB/IP host driver, which is run on the
+	  machine that is sharing the USB devices.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called usbip-host.
+
+config USBIP_VUDC
+	tristate "VUDC driver"
+	depends on USBIP_CORE && USB_GADGET
+	help
+	  This enables the USB/IP virtual USB device controller
+	  driver, which is run on the host machine, allowing the
+	  machine itself to act as a device.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called usbip-vudc.
+
+config USBIP_DEBUG
+	bool "Debug messages for USB/IP"
+	depends on USBIP_CORE
+	help
+	  This enables the debug messages from the USB/IP drivers.