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, 274 insertions, 0 deletions

diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
new file mode 100644
index 000000000..795fb41b4
--- /dev/null
+++ b/include/net/if_inet6.h
@@ -0,0 +1,274 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *	inet6 interface/address list definitions
+ *	Linux INET6 implementation 
+ *
+ *	Authors:
+ *	Pedro Roque		<roque@di.fc.ul.pt>	
+ */
+
+#ifndef _NET_IF_INET6_H
+#define _NET_IF_INET6_H
+
+#include <net/snmp.h>
+#include <linux/ipv6.h>
+#include <linux/refcount.h>
+
+/* inet6_dev.if_flags */
+
+#define IF_RA_OTHERCONF	0x80
+#define IF_RA_MANAGED	0x40
+#define IF_RA_RCVD	0x20
+#define IF_RS_SENT	0x10
+#define IF_READY	0x80000000
+
+enum {
+	INET6_IFADDR_STATE_PREDAD,
+	INET6_IFADDR_STATE_DAD,
+	INET6_IFADDR_STATE_POSTDAD,
+	INET6_IFADDR_STATE_ERRDAD,
+	INET6_IFADDR_STATE_DEAD,
+};
+
+struct inet6_ifaddr {
+	struct in6_addr		addr;
+	__u32			prefix_len;
+	__u32			rt_priority;
+
+	/* In seconds, relative to tstamp. Expiry is at tstamp + HZ * lft. */
+	__u32			valid_lft;
+	__u32			prefered_lft;
+	refcount_t		refcnt;
+	spinlock_t		lock;
+
+	int			state;
+
+	__u32			flags;
+	__u8			dad_probes;
+	__u8			stable_privacy_retry;
+
+	__u16			scope;
+	__u64			dad_nonce;
+
+	unsigned long		cstamp;	/* created timestamp */
+	unsigned long		tstamp; /* updated timestamp */
+
+	struct delayed_work	dad_work;
+
+	struct inet6_dev	*idev;
+	struct fib6_info	*rt;
+
+	struct hlist_node	addr_lst;
+	struct list_head	if_list;
+	/*
+	 * Used to safely traverse idev->addr_list in process context
+	 * if the idev->lock needed to protect idev->addr_list cannot be held.
+	 * In that case, add the items to this list temporarily and iterate
+	 * without holding idev->lock.
+	 * See addrconf_ifdown and dev_forward_change.
+	 */
+	struct list_head	if_list_aux;
+
+	struct list_head	tmp_list;
+	struct inet6_ifaddr	*ifpub;
+	int			regen_count;
+
+	bool			tokenized;
+
+	u8			ifa_proto;
+
+	struct rcu_head		rcu;
+	struct in6_addr		peer_addr;
+};
+
+struct ip6_sf_socklist {
+	unsigned int		sl_max;
+	unsigned int		sl_count;
+	struct rcu_head		rcu;
+	struct in6_addr		sl_addr[] __counted_by(sl_max);
+};
+
+struct ipv6_mc_socklist {
+	struct in6_addr		addr;
+	int			ifindex;
+	unsigned int		sfmode;		/* MCAST_{INCLUDE,EXCLUDE} */
+	struct ipv6_mc_socklist __rcu *next;
+	struct ip6_sf_socklist	__rcu *sflist;
+	struct rcu_head		rcu;
+};
+
+struct ip6_sf_list {
+	struct ip6_sf_list __rcu *sf_next;
+	struct in6_addr		sf_addr;
+	unsigned long		sf_count[2];	/* include/exclude counts */
+	unsigned char		sf_gsresp;	/* include in g & s response? */
+	unsigned char		sf_oldin;	/* change state */
+	unsigned char		sf_crcount;	/* retrans. left to send */
+	struct rcu_head		rcu;
+};
+
+#define MAF_TIMER_RUNNING	0x01
+#define MAF_LAST_REPORTER	0x02
+#define MAF_LOADED		0x04
+#define MAF_NOREPORT		0x08
+#define MAF_GSQUERY		0x10
+
+struct ifmcaddr6 {
+	struct in6_addr		mca_addr;
+	struct inet6_dev	*idev;
+	struct ifmcaddr6	__rcu *next;
+	struct ip6_sf_list	__rcu *mca_sources;
+	struct ip6_sf_list	__rcu *mca_tomb;
+	unsigned int		mca_sfmode;
+	unsigned char		mca_crcount;
+	unsigned long		mca_sfcount[2];
+	struct delayed_work	mca_work;
+	unsigned int		mca_flags;
+	int			mca_users;
+	refcount_t		mca_refcnt;
+	unsigned long		mca_cstamp;
+	unsigned long		mca_tstamp;
+	struct rcu_head		rcu;
+};
+
+/* Anycast stuff */
+
+struct ipv6_ac_socklist {
+	struct in6_addr		acl_addr;
+	int			acl_ifindex;
+	struct ipv6_ac_socklist *acl_next;
+};
+
+struct ifacaddr6 {
+	struct in6_addr		aca_addr;
+	struct fib6_info	*aca_rt;
+	struct ifacaddr6 __rcu	*aca_next;
+	struct hlist_node	aca_addr_lst;
+	int			aca_users;
+	refcount_t		aca_refcnt;
+	unsigned long		aca_cstamp;
+	unsigned long		aca_tstamp;
+	struct rcu_head		rcu;
+};
+
+#define	IFA_HOST	IPV6_ADDR_LOOPBACK
+#define	IFA_LINK	IPV6_ADDR_LINKLOCAL
+#define	IFA_SITE	IPV6_ADDR_SITELOCAL
+
+struct ipv6_devstat {
+	struct proc_dir_entry	*proc_dir_entry;
+	DEFINE_SNMP_STAT(struct ipstats_mib, ipv6);
+	DEFINE_SNMP_STAT_ATOMIC(struct icmpv6_mib_device, icmpv6dev);
+	DEFINE_SNMP_STAT_ATOMIC(struct icmpv6msg_mib_device, icmpv6msgdev);
+};
+
+struct inet6_dev {
+	struct net_device	*dev;
+	netdevice_tracker	dev_tracker;
+
+	struct list_head	addr_list;
+
+	struct ifmcaddr6	__rcu *mc_list;
+	struct ifmcaddr6	__rcu *mc_tomb;
+
+	unsigned char		mc_qrv;		/* Query Robustness Variable */
+	unsigned char		mc_gq_running;
+	unsigned char		mc_ifc_count;
+	unsigned char		mc_dad_count;
+
+	unsigned long		mc_v1_seen;	/* Max time we stay in MLDv1 mode */
+	unsigned long		mc_qi;		/* Query Interval */
+	unsigned long		mc_qri;		/* Query Response Interval */
+	unsigned long		mc_maxdelay;
+
+	struct delayed_work	mc_gq_work;	/* general query work */
+	struct delayed_work	mc_ifc_work;	/* interface change work */
+	struct delayed_work	mc_dad_work;	/* dad complete mc work */
+	struct delayed_work	mc_query_work;	/* mld query work */
+	struct delayed_work	mc_report_work;	/* mld report work */
+
+	struct sk_buff_head	mc_query_queue;		/* mld query queue */
+	struct sk_buff_head	mc_report_queue;	/* mld report queue */
+
+	spinlock_t		mc_query_lock;	/* mld query queue lock */
+	spinlock_t		mc_report_lock;	/* mld query report lock */
+	struct mutex		mc_lock;	/* mld global lock */
+
+	struct ifacaddr6 __rcu	*ac_list;
+	rwlock_t		lock;
+	refcount_t		refcnt;
+	__u32			if_flags;
+	int			dead;
+
+	u32			desync_factor;
+	struct list_head	tempaddr_list;
+
+	struct in6_addr		token;
+
+	struct neigh_parms	*nd_parms;
+	struct ipv6_devconf	cnf;
+	struct ipv6_devstat	stats;
+
+	struct timer_list	rs_timer;
+	__s32			rs_interval;	/* in jiffies */
+	__u8			rs_probes;
+
+	unsigned long		tstamp; /* ipv6InterfaceTable update timestamp */
+	struct rcu_head		rcu;
+
+	unsigned int		ra_mtu;
+};
+
+static inline void ipv6_eth_mc_map(const struct in6_addr *addr, char *buf)
+{
+	/*
+	 *	+-------+-------+-------+-------+-------+-------+
+	 *      |   33  |   33  | DST13 | DST14 | DST15 | DST16 |
+	 *      +-------+-------+-------+-------+-------+-------+
+	 */
+
+	buf[0]= 0x33;
+	buf[1]= 0x33;
+
+	memcpy(buf + 2, &addr->s6_addr32[3], sizeof(__u32));
+}
+
+static inline void ipv6_arcnet_mc_map(const struct in6_addr *addr, char *buf)
+{
+	buf[0] = 0x00;
+}
+
+static inline void ipv6_ib_mc_map(const struct in6_addr *addr,
+				  const unsigned char *broadcast, char *buf)
+{
+	unsigned char scope = broadcast[5] & 0xF;
+
+	buf[0]  = 0;		/* Reserved */
+	buf[1]  = 0xff;		/* Multicast QPN */
+	buf[2]  = 0xff;
+	buf[3]  = 0xff;
+	buf[4]  = 0xff;
+	buf[5]  = 0x10 | scope;	/* scope from broadcast address */
+	buf[6]  = 0x60;		/* IPv6 signature */
+	buf[7]  = 0x1b;
+	buf[8]  = broadcast[8];	/* P_Key */
+	buf[9]  = broadcast[9];
+	memcpy(buf + 10, addr->s6_addr + 6, 10);
+}
+
+static inline int ipv6_ipgre_mc_map(const struct in6_addr *addr,
+				    const unsigned char *broadcast, char *buf)
+{
+	if ((broadcast[0] | broadcast[1] | broadcast[2] | broadcast[3]) != 0) {
+		memcpy(buf, broadcast, 4);
+	} else {
+		/* v4mapped? */
+		if ((addr->s6_addr32[0] | addr->s6_addr32[1] |
+		     (addr->s6_addr32[2] ^ htonl(0x0000ffff))) != 0)
+			return -EINVAL;
+		memcpy(buf, &addr->s6_addr32[3], 4);
+	}
+	return 0;
+}
+
+#endif