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, 259 insertions, 0 deletions

diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
new file mode 100644
index 000000000..a40c2162a
--- /dev/null
+++ b/arch/powerpc/boot/ops.h
@@ -0,0 +1,259 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Global definition of all the bootwrapper operations.
+ *
+ * Author: Mark A. Greer <mgreer@mvista.com>
+ *
+ * 2006 (c) MontaVista Software, Inc.
+ */
+#ifndef _PPC_BOOT_OPS_H_
+#define _PPC_BOOT_OPS_H_
+
+#include <stddef.h>
+#include "types.h"
+#include "string.h"
+
+#define	BOOT_COMMAND_LINE_SIZE	2048
+#define	MAX_PATH_LEN		256
+#define	MAX_PROP_LEN		256 /* What should this be? */
+
+typedef void (*kernel_entry_t)(unsigned long r3, unsigned long r4, void *r5);
+
+/* Platform specific operations */
+struct platform_ops {
+	void	(*fixups)(void);
+	void	(*image_hdr)(const void *);
+	void *	(*malloc)(unsigned long size);
+	void	(*free)(void *ptr);
+	void *	(*realloc)(void *ptr, unsigned long size);
+	void	(*exit)(void);
+	void *	(*vmlinux_alloc)(unsigned long size);
+	void  	(*kentry)(unsigned long fdt_addr, void *vmlinux_addr);
+};
+extern struct platform_ops platform_ops;
+
+/* Device Tree operations */
+struct dt_ops {
+	void *	(*finddevice)(const char *name);
+	int	(*getprop)(const void *phandle, const char *name, void *buf,
+			const int buflen);
+	int	(*setprop)(const void *phandle, const char *name,
+			const void *buf, const int buflen);
+	int (*del_node)(const void *phandle);
+	void *(*get_parent)(const void *phandle);
+	/* The node must not already exist. */
+	void *(*create_node)(const void *parent, const char *name);
+	void *(*find_node_by_prop_value)(const void *prev,
+	                                 const char *propname,
+	                                 const char *propval, int proplen);
+	void *(*find_node_by_compatible)(const void *prev,
+	                                 const char *compat);
+	unsigned long (*finalize)(void);
+	char *(*get_path)(const void *phandle, char *buf, int len);
+};
+extern struct dt_ops dt_ops;
+
+/* Console operations */
+struct console_ops {
+	int	(*open)(void);
+	void	(*write)(const char *buf, int len);
+	void	(*edit_cmdline)(char *buf, int len, unsigned int getline_timeout);
+	void	(*close)(void);
+	void	*data;
+};
+extern struct console_ops console_ops;
+
+/* Serial console operations */
+struct serial_console_data {
+	int		(*open)(void);
+	void		(*putc)(unsigned char c);
+	unsigned char	(*getc)(void);
+	u8		(*tstc)(void);
+	void		(*close)(void);
+};
+
+struct loader_info {
+	void *promptr;
+	unsigned long initrd_addr, initrd_size;
+	char *cmdline;
+	int cmdline_len;
+};
+extern struct loader_info loader_info;
+
+void start(void);
+void fdt_init(void *blob);
+int serial_console_init(void);
+int ns16550_console_init(void *devp, struct serial_console_data *scdp);
+int cpm_console_init(void *devp, struct serial_console_data *scdp);
+int mpc5200_psc_console_init(void *devp, struct serial_console_data *scdp);
+int opal_console_init(void *devp, struct serial_console_data *scdp);
+void *simple_alloc_init(char *base, unsigned long heap_size,
+			unsigned long granularity, unsigned long max_allocs);
+extern void flush_cache(void *, unsigned long);
+int dt_xlate_reg(void *node, int res, unsigned long *addr, unsigned long *size);
+int dt_xlate_addr(void *node, u32 *buf, int buflen, unsigned long *xlated_addr);
+int dt_is_compatible(void *node, const char *compat);
+void dt_get_reg_format(void *node, u32 *naddr, u32 *nsize);
+int dt_get_virtual_reg(void *node, void **addr, int nres);
+
+static inline void *finddevice(const char *name)
+{
+	return (dt_ops.finddevice) ? dt_ops.finddevice(name) : NULL;
+}
+
+static inline int getprop(void *devp, const char *name, void *buf, int buflen)
+{
+	return (dt_ops.getprop) ? dt_ops.getprop(devp, name, buf, buflen) : -1;
+}
+
+static inline int setprop(void *devp, const char *name,
+                          const void *buf, int buflen)
+{
+	return (dt_ops.setprop) ? dt_ops.setprop(devp, name, buf, buflen) : -1;
+}
+#define setprop_val(devp, name, val) \
+	do { \
+		typeof(val) x = (val); \
+		setprop((devp), (name), &x, sizeof(x)); \
+	} while (0)
+
+static inline int setprop_str(void *devp, const char *name, const char *buf)
+{
+	if (dt_ops.setprop)
+		return dt_ops.setprop(devp, name, buf, strlen(buf) + 1);
+
+	return -1;
+}
+
+static inline int del_node(const void *devp)
+{
+	return dt_ops.del_node ? dt_ops.del_node(devp) : -1;
+}
+
+static inline void *get_parent(const char *devp)
+{
+	return dt_ops.get_parent ? dt_ops.get_parent(devp) : NULL;
+}
+
+static inline void *create_node(const void *parent, const char *name)
+{
+	return dt_ops.create_node ? dt_ops.create_node(parent, name) : NULL;
+}
+
+
+static inline void *find_node_by_prop_value(const void *prev,
+                                            const char *propname,
+                                            const char *propval, int proplen)
+{
+	if (dt_ops.find_node_by_prop_value)
+		return dt_ops.find_node_by_prop_value(prev, propname,
+		                                      propval, proplen);
+
+	return NULL;
+}
+
+static inline void *find_node_by_prop_value_str(const void *prev,
+                                                const char *propname,
+                                                const char *propval)
+{
+	return find_node_by_prop_value(prev, propname, propval,
+	                               strlen(propval) + 1);
+}
+
+static inline void *find_node_by_devtype(const void *prev,
+                                         const char *type)
+{
+	return find_node_by_prop_value_str(prev, "device_type", type);
+}
+
+static inline void *find_node_by_alias(const char *alias)
+{
+	void *devp = finddevice("/aliases");
+
+	if (devp) {
+		char path[MAX_PATH_LEN];
+		if (getprop(devp, alias, path, MAX_PATH_LEN) > 0)
+			return finddevice(path);
+	}
+
+	return NULL;
+}
+
+static inline void *find_node_by_compatible(const void *prev,
+                                            const char *compat)
+{
+	if (dt_ops.find_node_by_compatible)
+		return dt_ops.find_node_by_compatible(prev, compat);
+
+	return NULL;
+}
+
+void dt_fixup_memory(u64 start, u64 size);
+void dt_fixup_cpu_clocks(u32 cpufreq, u32 tbfreq, u32 busfreq);
+void dt_fixup_clock(const char *path, u32 freq);
+void dt_fixup_mac_address_by_alias(const char *alias, const u8 *addr);
+void dt_fixup_mac_address(u32 index, const u8 *addr);
+void __dt_fixup_mac_addresses(u32 startindex, ...);
+#define dt_fixup_mac_addresses(...) \
+	__dt_fixup_mac_addresses(0, __VA_ARGS__, NULL)
+
+
+static inline char *get_path(const void *phandle, char *buf, int len)
+{
+	if (dt_ops.get_path)
+		return dt_ops.get_path(phandle, buf, len);
+
+	return NULL;
+}
+
+static inline void *malloc(unsigned long size)
+{
+	return (platform_ops.malloc) ? platform_ops.malloc(size) : NULL;
+}
+
+static inline void free(void *ptr)
+{
+	if (platform_ops.free)
+		platform_ops.free(ptr);
+}
+
+static inline void exit(void)
+{
+	if (platform_ops.exit)
+		platform_ops.exit();
+	for(;;);
+}
+#define fatal(args...) { printf(args); exit(); }
+
+
+#define BSS_STACK(size) \
+	static char _bss_stack[size]; \
+	void *_platform_stack_top = _bss_stack + sizeof(_bss_stack);
+
+extern unsigned long timebase_period_ns;
+void udelay(long delay);
+
+extern char _start[];
+extern char __bss_start[];
+extern char _end[];
+extern char _vmlinux_start[];
+extern char _vmlinux_end[];
+extern char _initrd_start[];
+extern char _initrd_end[];
+extern char _dtb_start[];
+extern char _dtb_end[];
+extern char _esm_blob_start[];
+extern char _esm_blob_end[];
+
+static inline __attribute__((const))
+int __ilog2_u32(u32 n)
+{
+	int bit;
+	asm ("cntlzw %0,%1" : "=r" (bit) : "r" (n));
+	return 31 - bit;
+}
+
+long partial_decompress(void *inbuf, unsigned long input_size, void *outbuf,
+	unsigned long output_size, unsigned long skip);
+
+#endif /* _PPC_BOOT_OPS_H_ */