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, 55 insertions, 0 deletions

diff --git a/drivers/usb/image/microtek.h b/drivers/usb/image/microtek.h
new file mode 100644
index 000000000..7bd5f4639
--- /dev/null
+++ b/drivers/usb/image/microtek.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+ /*
+ * Driver for Microtek Scanmaker X6 USB scanner and possibly others.
+ * 
+ * (C) Copyright 2000 John Fremlin <vii@penguinpowered.com>
+ * (C) Copyright 2000 Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>
+ *
+ * See microtek.c for history
+ *
+ */
+
+typedef void (*mts_scsi_cmnd_callback)(struct scsi_cmnd *);
+
+
+struct mts_transfer_context
+{
+	struct mts_desc *instance;
+	mts_scsi_cmnd_callback final_callback;
+	struct scsi_cmnd *srb;
+	
+	void *data;
+	unsigned data_length;
+	int data_pipe;
+	struct scatterlist *curr_sg;
+
+	u8 *scsi_status; /* status returned from ep_response after command completion */
+};
+
+
+struct mts_desc {
+	struct mts_desc *next;
+	struct mts_desc *prev;
+
+	struct usb_device *usb_dev;
+	struct usb_interface *usb_intf;
+
+	/* Endpoint addresses */
+	u8 ep_out;
+	u8 ep_response;
+	u8 ep_image;
+
+	struct Scsi_Host *host;
+
+	struct urb *urb;
+	struct mts_transfer_context context;
+};
+
+
+#define MTS_EP_OUT	0x1
+#define MTS_EP_RESPONSE	0x2
+#define MTS_EP_IMAGE	0x3
+#define MTS_EP_TOTAL	0x3
+
+#define MTS_SCSI_ERR_MASK ~0x3fu
+