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, 101 insertions, 0 deletions

diff --git a/drivers/video/fbdev/sa1100fb.h b/drivers/video/fbdev/sa1100fb.h
new file mode 100644
index 000000000..b4363444f
--- /dev/null
+++ b/drivers/video/fbdev/sa1100fb.h
@@ -0,0 +1,101 @@
+/*
+ * linux/drivers/video/sa1100fb.h
+ *    -- StrongARM 1100 LCD Controller Frame Buffer Device
+ *
+ *  Copyright (C) 1999 Eric A. Thomas
+ *   Based on acornfb.c Copyright (C) Russell King.
+ *  
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+struct gpio_desc;
+
+#define LCCR0           0x0000          /* LCD Control Reg. 0 */
+#define LCSR            0x0004          /* LCD Status Reg. */
+#define DBAR1           0x0010          /* LCD DMA Base Address Reg. channel 1 */
+#define DCAR1           0x0014          /* LCD DMA Current Address Reg. channel 1 */
+#define DBAR2           0x0018          /* LCD DMA Base Address Reg.  channel 2 */
+#define DCAR2           0x001C          /* LCD DMA Current Address Reg. channel 2 */
+#define LCCR1           0x0020          /* LCD Control Reg. 1 */
+#define LCCR2           0x0024          /* LCD Control Reg. 2 */
+#define LCCR3           0x0028          /* LCD Control Reg. 3 */
+
+/* Shadows for LCD controller registers */
+struct sa1100fb_lcd_reg {
+	unsigned long lccr0;
+	unsigned long lccr1;
+	unsigned long lccr2;
+	unsigned long lccr3;
+};
+
+struct sa1100fb_info {
+	struct fb_info		fb;
+	struct device		*dev;
+	const struct sa1100fb_rgb *rgb[NR_RGB];
+	void __iomem		*base;
+	struct gpio_desc	*shannon_lcden;
+
+	/*
+	 * These are the addresses we mapped
+	 * the framebuffer memory region to.
+	 */
+	dma_addr_t		map_dma;
+	u_char *		map_cpu;
+	u_int			map_size;
+
+	u_char *		screen_cpu;
+	dma_addr_t		screen_dma;
+	u16 *			palette_cpu;
+	dma_addr_t		palette_dma;
+	u_int			palette_size;
+
+	dma_addr_t		dbar1;
+	dma_addr_t		dbar2;
+
+	u_int			reg_lccr0;
+	u_int			reg_lccr1;
+	u_int			reg_lccr2;
+	u_int			reg_lccr3;
+
+	volatile u_char		state;
+	volatile u_char		task_state;
+	struct mutex		ctrlr_lock;
+	wait_queue_head_t	ctrlr_wait;
+	struct work_struct	task;
+
+#ifdef CONFIG_CPU_FREQ
+	struct notifier_block	freq_transition;
+#endif
+
+	const struct sa1100fb_mach_info *inf;
+	struct clk *clk;
+
+	u32 pseudo_palette[16];
+};
+
+#define TO_INF(ptr,member)	container_of(ptr,struct sa1100fb_info,member)
+
+#define SA1100_PALETTE_MODE_VAL(bpp)    (((bpp) & 0x018) << 9)
+
+/*
+ * These are the actions for set_ctrlr_state
+ */
+#define C_DISABLE		(0)
+#define C_ENABLE		(1)
+#define C_DISABLE_CLKCHANGE	(2)
+#define C_ENABLE_CLKCHANGE	(3)
+#define C_REENABLE		(4)
+#define C_DISABLE_PM		(5)
+#define C_ENABLE_PM		(6)
+#define C_STARTUP		(7)
+
+#define SA1100_NAME	"SA1100"
+
+/*
+ * Minimum X and Y resolutions
+ */
+#define MIN_XRES	64
+#define MIN_YRES	64
+