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, 109 insertions, 0 deletions

diff --git a/Documentation/driver-api/infiniband.rst b/Documentation/driver-api/infiniband.rst
new file mode 100644
index 000000000..d48f24677
--- /dev/null
+++ b/Documentation/driver-api/infiniband.rst
@@ -0,0 +1,109 @@
+===========================================
+InfiniBand and Remote DMA (RDMA) Interfaces
+===========================================
+
+Introduction and Overview
+=========================
+
+TBD
+
+InfiniBand core interfaces
+==========================
+
+.. kernel-doc:: drivers/infiniband/core/iwpm_util.h
+    :internal:
+
+.. kernel-doc:: drivers/infiniband/core/cq.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/cm.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/rw.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/device.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/verbs.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/packer.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/sa_query.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/ud_header.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/umem.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/core/umem_odp.c
+    :export:
+
+RDMA Verbs transport library
+============================
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/mr.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/rc.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/ah.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/vt.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/cq.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/qp.c
+    :export:
+
+.. kernel-doc:: drivers/infiniband/sw/rdmavt/mcast.c
+    :export:
+
+Upper Layer Protocols
+=====================
+
+iSCSI Extensions for RDMA (iSER)
+--------------------------------
+
+.. kernel-doc:: drivers/infiniband/ulp/iser/iscsi_iser.h
+   :internal:
+
+.. kernel-doc:: drivers/infiniband/ulp/iser/iscsi_iser.c
+   :functions: iscsi_iser_pdu_alloc iser_initialize_task_headers
+               iscsi_iser_task_init iscsi_iser_mtask_xmit iscsi_iser_task_xmit
+               iscsi_iser_cleanup_task iscsi_iser_check_protection
+               iscsi_iser_conn_create iscsi_iser_conn_bind
+               iscsi_iser_conn_start iscsi_iser_conn_stop
+               iscsi_iser_session_destroy iscsi_iser_session_create
+               iscsi_iser_set_param iscsi_iser_ep_connect iscsi_iser_ep_poll
+               iscsi_iser_ep_disconnect
+
+.. kernel-doc:: drivers/infiniband/ulp/iser/iser_initiator.c
+   :internal:
+
+.. kernel-doc:: drivers/infiniband/ulp/iser/iser_verbs.c
+   :internal:
+
+InfiniBand SCSI RDMA protocol target support
+--------------------------------------------
+
+.. kernel-doc:: drivers/infiniband/ulp/srpt/ib_srpt.h
+   :internal:
+
+.. kernel-doc:: drivers/infiniband/ulp/srpt/ib_srpt.c
+   :internal:
+
+iSCSI Extensions for RDMA (iSER) target support
+-----------------------------------------------
+
+.. kernel-doc:: drivers/infiniband/ulp/isert/ib_isert.c
+   :internal:
+