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, 46 insertions, 0 deletions

diff --git a/include/net/ax88796.h b/include/net/ax88796.h
new file mode 100644
index 000000000..303100f08
--- /dev/null
+++ b/include/net/ax88796.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* include/net/ax88796.h
+ *
+ * Copyright 2005 Simtec Electronics
+ *	Ben Dooks <ben@simtec.co.uk>
+*/
+
+#ifndef __NET_AX88796_PLAT_H
+#define __NET_AX88796_PLAT_H
+
+#include <linux/types.h>
+
+struct sk_buff;
+struct net_device;
+struct platform_device;
+
+#define AXFLG_HAS_EEPROM		(1<<0)
+#define AXFLG_MAC_FROMDEV		(1<<1)	/* device already has MAC */
+#define AXFLG_HAS_93CX6			(1<<2)	/* use eeprom_93cx6 driver */
+#define AXFLG_MAC_FROMPLATFORM		(1<<3)	/* MAC given by platform data */
+
+struct ax_plat_data {
+	unsigned int	 flags;
+	unsigned char	 wordlength;	/* 1 or 2 */
+	unsigned char	 dcr_val;	/* default value for DCR */
+	unsigned char	 rcr_val;	/* default value for RCR */
+	unsigned char	 gpoc_val;	/* default value for GPOC */
+	u32		*reg_offsets;	/* register offsets */
+	u8		*mac_addr;	/* MAC addr (only used when
+					   AXFLG_MAC_FROMPLATFORM is used */
+
+	/* uses default ax88796 buffer if set to NULL */
+	void (*block_output)(struct net_device *dev, int count,
+			const unsigned char *buf, int star_page);
+	void (*block_input)(struct net_device *dev, int count,
+			struct sk_buff *skb, int ring_offset);
+	/* returns nonzero if a pending interrupt request might be caused by
+	 * the ax88796. Handles all interrupts if set to NULL
+	 */
+	int (*check_irq)(struct platform_device *pdev);
+};
+
+/* exported from ax88796.c for xsurf100.c  */
+extern void ax_NS8390_reinit(struct net_device *dev);
+
+#endif /* __NET_AX88796_PLAT_H */