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, 339 insertions, 0 deletions

diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
new file mode 100644
index 000000000..c3806c6ac
--- /dev/null
+++ b/net/ipv6/Kconfig
@@ -0,0 +1,339 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# IPv6 configuration
+#
+
+menuconfig IPV6
+	bool "The IPv6 protocol"
+	default y
+	select CRYPTO_LIB_SHA1
+	help
+	  Support for IP version 6 (IPv6).
+
+	  For general information about IPv6, see
+	  <https://en.wikipedia.org/wiki/IPv6>.
+	  For specific information about IPv6 under Linux, see
+	  Documentation/networking/ipv6.rst and read the HOWTO at
+	  <https://www.tldp.org/HOWTO/Linux+IPv6-HOWTO/>
+
+if IPV6
+
+config IPV6_ROUTER_PREF
+	bool "IPv6: Router Preference (RFC 4191) support"
+	help
+	  Router Preference is an optional extension to the Router
+	  Advertisement message which improves the ability of hosts
+	  to pick an appropriate router, especially when the hosts
+	  are placed in a multi-homed network.
+
+	  If unsure, say N.
+
+config IPV6_ROUTE_INFO
+	bool "IPv6: Route Information (RFC 4191) support"
+	depends on IPV6_ROUTER_PREF
+	help
+	  Support of Route Information.
+
+	  If unsure, say N.
+
+config IPV6_OPTIMISTIC_DAD
+	bool "IPv6: Enable RFC 4429 Optimistic DAD"
+	help
+	  Support for optimistic Duplicate Address Detection. It allows for
+	  autoconfigured addresses to be used more quickly.
+
+	  If unsure, say N.
+
+config INET6_AH
+	tristate "IPv6: AH transformation"
+	select XFRM_AH
+	help
+	  Support for IPsec AH (Authentication Header).
+
+	  AH can be used with various authentication algorithms.  Besides
+	  enabling AH support itself, this option enables the generic
+	  implementations of the algorithms that RFC 8221 lists as MUST be
+	  implemented.  If you need any other algorithms, you'll need to enable
+	  them in the crypto API.  You should also enable accelerated
+	  implementations of any needed algorithms when available.
+
+	  If unsure, say Y.
+
+config INET6_ESP
+	tristate "IPv6: ESP transformation"
+	select XFRM_ESP
+	help
+	  Support for IPsec ESP (Encapsulating Security Payload).
+
+	  ESP can be used with various encryption and authentication algorithms.
+	  Besides enabling ESP support itself, this option enables the generic
+	  implementations of the algorithms that RFC 8221 lists as MUST be
+	  implemented.  If you need any other algorithms, you'll need to enable
+	  them in the crypto API.  You should also enable accelerated
+	  implementations of any needed algorithms when available.
+
+	  If unsure, say Y.
+
+config INET6_ESP_OFFLOAD
+	tristate "IPv6: ESP transformation offload"
+	depends on INET6_ESP
+	select XFRM_OFFLOAD
+	default n
+	help
+	  Support for ESP transformation offload. This makes sense
+	  only if this system really does IPsec and want to do it
+	  with high throughput. A typical desktop system does not
+	  need it, even if it does IPsec.
+
+	  If unsure, say N.
+
+config INET6_ESPINTCP
+	bool "IPv6: ESP in TCP encapsulation (RFC 8229)"
+	depends on XFRM && INET6_ESP
+	select STREAM_PARSER
+	select NET_SOCK_MSG
+	select XFRM_ESPINTCP
+	help
+	  Support for RFC 8229 encapsulation of ESP and IKE over
+	  TCP/IPv6 sockets.
+
+	  If unsure, say N.
+
+config INET6_IPCOMP
+	tristate "IPv6: IPComp transformation"
+	select INET6_XFRM_TUNNEL
+	select XFRM_IPCOMP
+	help
+	  Support for IP Payload Compression Protocol (IPComp) (RFC3173),
+	  typically needed for IPsec.
+
+	  If unsure, say Y.
+
+config IPV6_MIP6
+	tristate "IPv6: Mobility"
+	select XFRM
+	help
+	  Support for IPv6 Mobility described in RFC 3775.
+
+	  If unsure, say N.
+
+config IPV6_ILA
+	tristate "IPv6: Identifier Locator Addressing (ILA)"
+	depends on NETFILTER
+	select DST_CACHE
+	select LWTUNNEL
+	help
+	  Support for IPv6 Identifier Locator Addressing (ILA).
+
+	  ILA is a mechanism to do network virtualization without
+	  encapsulation. The basic concept of ILA is that we split an
+	  IPv6 address into a 64 bit locator and 64 bit identifier. The
+	  identifier is the identity of an entity in communication
+	  ("who") and the locator expresses the location of the
+	  entity ("where").
+
+	  ILA can be configured using the "encap ila" option with
+	  "ip -6 route" command. ILA is described in
+	  https://tools.ietf.org/html/draft-herbert-nvo3-ila-00.
+
+	  If unsure, say N.
+
+config INET6_XFRM_TUNNEL
+	tristate
+	select INET6_TUNNEL
+	default n
+
+config INET6_TUNNEL
+	tristate
+	default n
+
+config IPV6_VTI
+	tristate "Virtual (secure) IPv6: tunneling"
+	select IPV6_TUNNEL
+	select NET_IP_TUNNEL
+	select XFRM
+	help
+	Tunneling means encapsulating data of one protocol type within
+	another protocol and sending it over a channel that understands the
+	encapsulating protocol. This can be used with xfrm mode tunnel to give
+	the notion of a secure tunnel for IPSEC and then use routing protocol
+	on top.
+
+config IPV6_SIT
+	tristate "IPv6: IPv6-in-IPv4 tunnel (SIT driver)"
+	select INET_TUNNEL
+	select NET_IP_TUNNEL
+	select IPV6_NDISC_NODETYPE
+	default m
+	help
+	  Tunneling means encapsulating data of one protocol type within
+	  another protocol and sending it over a channel that understands the
+	  encapsulating protocol. This driver implements encapsulation of IPv6
+	  into IPv4 packets. This is useful if you want to connect two IPv6
+	  networks over an IPv4-only path.
+
+	  Saying M here will produce a module called sit. If unsure, say M.
+
+config IPV6_SIT_6RD
+	bool "IPv6: IPv6 Rapid Deployment (6RD)"
+	depends on IPV6_SIT
+	default n
+	help
+	  IPv6 Rapid Deployment (6rd; draft-ietf-softwire-ipv6-6rd) builds upon
+	  mechanisms of 6to4 (RFC3056) to enable a service provider to rapidly
+	  deploy IPv6 unicast service to IPv4 sites to which it provides
+	  customer premise equipment.  Like 6to4, it utilizes stateless IPv6 in
+	  IPv4 encapsulation in order to transit IPv4-only network
+	  infrastructure.  Unlike 6to4, a 6rd service provider uses an IPv6
+	  prefix of its own in place of the fixed 6to4 prefix.
+
+	  With this option enabled, the SIT driver offers 6rd functionality by
+	  providing additional ioctl API to configure the IPv6 Prefix for in
+	  stead of static 2002::/16 for 6to4.
+
+	  If unsure, say N.
+
+config IPV6_NDISC_NODETYPE
+	bool
+
+config IPV6_TUNNEL
+	tristate "IPv6: IP-in-IPv6 tunnel (RFC2473)"
+	select INET6_TUNNEL
+	select DST_CACHE
+	select GRO_CELLS
+	help
+	  Support for IPv6-in-IPv6 and IPv4-in-IPv6 tunnels described in
+	  RFC 2473.
+
+	  If unsure, say N.
+
+config IPV6_GRE
+	tristate "IPv6: GRE tunnel"
+	select IPV6_TUNNEL
+	select NET_IP_TUNNEL
+	depends on NET_IPGRE_DEMUX
+	help
+	  Tunneling means encapsulating data of one protocol type within
+	  another protocol and sending it over a channel that understands the
+	  encapsulating protocol. This particular tunneling driver implements
+	  GRE (Generic Routing Encapsulation) and at this time allows
+	  encapsulating of IPv4 or IPv6 over existing IPv6 infrastructure.
+	  This driver is useful if the other endpoint is a Cisco router: Cisco
+	  likes GRE much better than the other Linux tunneling driver ("IP
+	  tunneling" above). In addition, GRE allows multicast redistribution
+	  through the tunnel.
+
+	  Saying M here will produce a module called ip6_gre. If unsure, say N.
+
+config IPV6_FOU
+	tristate
+	default NET_FOU && IPV6
+
+config IPV6_FOU_TUNNEL
+	tristate
+	default NET_FOU_IP_TUNNELS && IPV6_FOU
+	select IPV6_TUNNEL
+
+config IPV6_MULTIPLE_TABLES
+	bool "IPv6: Multiple Routing Tables"
+	select FIB_RULES
+	help
+	  Support multiple routing tables.
+
+config IPV6_SUBTREES
+	bool "IPv6: source address based routing"
+	depends on IPV6_MULTIPLE_TABLES
+	help
+	  Enable routing by source address or prefix.
+
+	  The destination address is still the primary routing key, so mixing
+	  normal and source prefix specific routes in the same routing table
+	  may sometimes lead to unintended routing behavior.  This can be
+	  avoided by defining different routing tables for the normal and
+	  source prefix specific routes.
+
+	  If unsure, say N.
+
+config IPV6_MROUTE
+	bool "IPv6: multicast routing"
+	depends on IPV6
+	select IP_MROUTE_COMMON
+	help
+	  Support for IPv6 multicast forwarding.
+	  If unsure, say N.
+
+config IPV6_MROUTE_MULTIPLE_TABLES
+	bool "IPv6: multicast policy routing"
+	depends on IPV6_MROUTE
+	select FIB_RULES
+	help
+	  Normally, a multicast router runs a userspace daemon and decides
+	  what to do with a multicast packet based on the source and
+	  destination addresses. If you say Y here, the multicast router
+	  will also be able to take interfaces and packet marks into
+	  account and run multiple instances of userspace daemons
+	  simultaneously, each one handling a single table.
+
+	  If unsure, say N.
+
+config IPV6_PIMSM_V2
+	bool "IPv6: PIM-SM version 2 support"
+	depends on IPV6_MROUTE
+	help
+	  Support for IPv6 PIM multicast routing protocol PIM-SMv2.
+	  If unsure, say N.
+
+config IPV6_SEG6_LWTUNNEL
+	bool "IPv6: Segment Routing Header encapsulation support"
+	depends on IPV6
+	select LWTUNNEL
+	select DST_CACHE
+	select IPV6_MULTIPLE_TABLES
+	help
+	  Support for encapsulation of packets within an outer IPv6
+	  header and a Segment Routing Header using the lightweight
+	  tunnels mechanism. Also enable support for advanced local
+	  processing of SRv6 packets based on their active segment.
+
+	  If unsure, say N.
+
+config IPV6_SEG6_HMAC
+	bool "IPv6: Segment Routing HMAC support"
+	depends on IPV6
+	select CRYPTO_LIB_SHA1
+	select CRYPTO_LIB_SHA256
+	select CRYPTO_LIB_UTILS
+	help
+	  Support for HMAC signature generation and verification
+	  of SR-enabled packets.
+
+	  If unsure, say N.
+
+config IPV6_SEG6_BPF
+	def_bool y
+	depends on IPV6_SEG6_LWTUNNEL
+	depends on IPV6 = y
+
+config IPV6_RPL_LWTUNNEL
+	bool "IPv6: RPL Source Routing Header support"
+	depends on IPV6
+	select LWTUNNEL
+	select DST_CACHE
+	help
+	  Support for RFC6554 RPL Source Routing Header using the lightweight
+	  tunnels mechanism.
+
+	  If unsure, say N.
+
+config IPV6_IOAM6_LWTUNNEL
+	bool "IPv6: IOAM Pre-allocated Trace insertion support"
+	depends on IPV6
+	select LWTUNNEL
+	select DST_CACHE
+	help
+	  Support for the insertion of IOAM Pre-allocated Trace
+	  Header using the lightweight tunnels mechanism.
+
+	  If unsure, say N.
+
+endif # IPV6