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

2 files changed, 184 insertions, 0 deletions

diff --git a/Documentation/gpu/imagination/index.rst b/Documentation/gpu/imagination/index.rst
new file mode 100644
index 000000000..0c1e247ce
--- /dev/null
+++ b/Documentation/gpu/imagination/index.rst
@@ -0,0 +1,13 @@
+=======================================
+drm/imagination PowerVR Graphics Driver
+=======================================
+
+.. kernel-doc:: drivers/gpu/drm/imagination/pvr_drv.c
+   :doc: PowerVR (Series 6 and later) and IMG Graphics Driver
+
+Contents
+========
+.. toctree::
+   :maxdepth: 2
+
+   uapi
diff --git a/Documentation/gpu/imagination/uapi.rst b/Documentation/gpu/imagination/uapi.rst
new file mode 100644
index 000000000..7502413d0
--- /dev/null
+++ b/Documentation/gpu/imagination/uapi.rst
@@ -0,0 +1,171 @@
+====
+UAPI
+====
+The sources associated with this section can be found in ``pvr_drm.h``.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR UAPI
+
+OBJECT ARRAYS
+=============
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_obj_array
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: DRM_PVR_OBJ_ARRAY
+
+IOCTLS
+======
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL interface
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: PVR_IOCTL
+
+DEV_QUERY
+---------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL DEV_QUERY interface
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_dev_query
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_dev_query_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_dev_query_gpu_info
+                 drm_pvr_dev_query_runtime_info
+                 drm_pvr_dev_query_hwrt_info
+                 drm_pvr_dev_query_quirks
+                 drm_pvr_dev_query_enhancements
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_heap_id
+                 drm_pvr_heap
+                 drm_pvr_dev_query_heap_info
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_static_data_area_usage
+                 drm_pvr_static_data_area
+                 drm_pvr_dev_query_static_data_areas
+
+CREATE_BO
+---------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL CREATE_BO interface
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_create_bo_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for CREATE_BO
+
+GET_BO_MMAP_OFFSET
+------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL GET_BO_MMAP_OFFSET interface
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_get_bo_mmap_offset_args
+
+CREATE_VM_CONTEXT and DESTROY_VM_CONTEXT
+----------------------------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL CREATE_VM_CONTEXT and DESTROY_VM_CONTEXT interfaces
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_create_vm_context_args
+                 drm_pvr_ioctl_destroy_vm_context_args
+
+VM_MAP and VM_UNMAP
+-------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL VM_MAP and VM_UNMAP interfaces
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_vm_map_args
+                 drm_pvr_ioctl_vm_unmap_args
+
+CREATE_CONTEXT and DESTROY_CONTEXT
+----------------------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL CREATE_CONTEXT and DESTROY_CONTEXT interfaces
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_create_context_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ctx_priority
+                 drm_pvr_ctx_type
+                 drm_pvr_static_render_context_state
+                 drm_pvr_static_render_context_state_format
+                 drm_pvr_reset_framework
+                 drm_pvr_reset_framework_format
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_destroy_context_args
+
+CREATE_FREE_LIST and DESTROY_FREE_LIST
+--------------------------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL CREATE_FREE_LIST and DESTROY_FREE_LIST interfaces
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_create_free_list_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_destroy_free_list_args
+
+CREATE_HWRT_DATASET and DESTROY_HWRT_DATASET
+--------------------------------------------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL CREATE_HWRT_DATASET and DESTROY_HWRT_DATASET interfaces
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_create_hwrt_dataset_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_create_hwrt_geom_data_args
+                 drm_pvr_create_hwrt_rt_data_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_destroy_hwrt_dataset_args
+
+SUBMIT_JOBS
+-----------
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: PowerVR IOCTL SUBMIT_JOBS interface
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for the drm_pvr_sync_op object.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_ioctl_submit_jobs_args
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for SUBMIT_JOB ioctl geometry command.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for SUBMIT_JOB ioctl fragment command.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for SUBMIT_JOB ioctl compute command.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :doc: Flags for SUBMIT_JOB ioctl transfer command.
+
+.. kernel-doc:: include/uapi/drm/pvr_drm.h
+   :identifiers: drm_pvr_sync_op
+                 drm_pvr_job_type
+                 drm_pvr_hwrt_data_ref
+                 drm_pvr_job
+
+Internal notes
+==============
+.. kernel-doc:: drivers/gpu/drm/imagination/pvr_device.h
+   :doc: IOCTL validation helpers
+
+.. kernel-doc:: drivers/gpu/drm/imagination/pvr_device.h
+   :identifiers: PVR_STATIC_ASSERT_64BIT_ALIGNED PVR_IOCTL_UNION_PADDING_CHECK
+                 pvr_ioctl_union_padding_check