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, 164 insertions, 0 deletions

diff --git a/include/drm/drm_eld.h b/include/drm/drm_eld.h
new file mode 100644
index 000000000..0a88d10b2
--- /dev/null
+++ b/include/drm/drm_eld.h
@@ -0,0 +1,164 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2023 Intel Corporation
+ */
+
+#ifndef __DRM_ELD_H__
+#define __DRM_ELD_H__
+
+#include <linux/types.h>
+
+struct cea_sad;
+
+/* ELD Header Block */
+#define DRM_ELD_HEADER_BLOCK_SIZE	4
+
+#define DRM_ELD_VER			0
+# define DRM_ELD_VER_SHIFT		3
+# define DRM_ELD_VER_MASK		(0x1f << 3)
+# define DRM_ELD_VER_CEA861D		(2 << 3) /* supports 861D or below */
+# define DRM_ELD_VER_CANNED		(0x1f << 3)
+
+#define DRM_ELD_BASELINE_ELD_LEN	2	/* in dwords! */
+
+/* ELD Baseline Block for ELD_Ver == 2 */
+#define DRM_ELD_CEA_EDID_VER_MNL	4
+# define DRM_ELD_CEA_EDID_VER_SHIFT	5
+# define DRM_ELD_CEA_EDID_VER_MASK	(7 << 5)
+# define DRM_ELD_CEA_EDID_VER_NONE	(0 << 5)
+# define DRM_ELD_CEA_EDID_VER_CEA861	(1 << 5)
+# define DRM_ELD_CEA_EDID_VER_CEA861A	(2 << 5)
+# define DRM_ELD_CEA_EDID_VER_CEA861BCD	(3 << 5)
+# define DRM_ELD_MNL_SHIFT		0
+# define DRM_ELD_MNL_MASK		(0x1f << 0)
+
+#define DRM_ELD_SAD_COUNT_CONN_TYPE	5
+# define DRM_ELD_SAD_COUNT_SHIFT	4
+# define DRM_ELD_SAD_COUNT_MASK		(0xf << 4)
+# define DRM_ELD_CONN_TYPE_SHIFT	2
+# define DRM_ELD_CONN_TYPE_MASK		(3 << 2)
+# define DRM_ELD_CONN_TYPE_HDMI		(0 << 2)
+# define DRM_ELD_CONN_TYPE_DP		(1 << 2)
+# define DRM_ELD_SUPPORTS_AI		(1 << 1)
+# define DRM_ELD_SUPPORTS_HDCP		(1 << 0)
+
+#define DRM_ELD_AUD_SYNCH_DELAY		6	/* in units of 2 ms */
+# define DRM_ELD_AUD_SYNCH_DELAY_MAX	0xfa	/* 500 ms */
+
+#define DRM_ELD_SPEAKER			7
+# define DRM_ELD_SPEAKER_MASK		0x7f
+# define DRM_ELD_SPEAKER_RLRC		(1 << 6)
+# define DRM_ELD_SPEAKER_FLRC		(1 << 5)
+# define DRM_ELD_SPEAKER_RC		(1 << 4)
+# define DRM_ELD_SPEAKER_RLR		(1 << 3)
+# define DRM_ELD_SPEAKER_FC		(1 << 2)
+# define DRM_ELD_SPEAKER_LFE		(1 << 1)
+# define DRM_ELD_SPEAKER_FLR		(1 << 0)
+
+#define DRM_ELD_PORT_ID			8	/* offsets 8..15 inclusive */
+# define DRM_ELD_PORT_ID_LEN		8
+
+#define DRM_ELD_MANUFACTURER_NAME0	16
+#define DRM_ELD_MANUFACTURER_NAME1	17
+
+#define DRM_ELD_PRODUCT_CODE0		18
+#define DRM_ELD_PRODUCT_CODE1		19
+
+#define DRM_ELD_MONITOR_NAME_STRING	20	/* offsets 20..(20+mnl-1) inclusive */
+
+#define DRM_ELD_CEA_SAD(mnl, sad)	(20 + (mnl) + 3 * (sad))
+
+/**
+ * drm_eld_mnl - Get ELD monitor name length in bytes.
+ * @eld: pointer to an eld memory structure with mnl set
+ */
+static inline int drm_eld_mnl(const u8 *eld)
+{
+	return (eld[DRM_ELD_CEA_EDID_VER_MNL] & DRM_ELD_MNL_MASK) >> DRM_ELD_MNL_SHIFT;
+}
+
+int drm_eld_sad_get(const u8 *eld, int sad_index, struct cea_sad *cta_sad);
+int drm_eld_sad_set(u8 *eld, int sad_index, const struct cea_sad *cta_sad);
+
+/**
+ * drm_eld_sad - Get ELD SAD structures.
+ * @eld: pointer to an eld memory structure with sad_count set
+ */
+static inline const u8 *drm_eld_sad(const u8 *eld)
+{
+	unsigned int ver, mnl;
+
+	ver = (eld[DRM_ELD_VER] & DRM_ELD_VER_MASK) >> DRM_ELD_VER_SHIFT;
+	if (ver != 2 && ver != 31)
+		return NULL;
+
+	mnl = drm_eld_mnl(eld);
+	if (mnl > 16)
+		return NULL;
+
+	return eld + DRM_ELD_CEA_SAD(mnl, 0);
+}
+
+/**
+ * drm_eld_sad_count - Get ELD SAD count.
+ * @eld: pointer to an eld memory structure with sad_count set
+ */
+static inline int drm_eld_sad_count(const u8 *eld)
+{
+	return (eld[DRM_ELD_SAD_COUNT_CONN_TYPE] & DRM_ELD_SAD_COUNT_MASK) >>
+		DRM_ELD_SAD_COUNT_SHIFT;
+}
+
+/**
+ * drm_eld_calc_baseline_block_size - Calculate baseline block size in bytes
+ * @eld: pointer to an eld memory structure with mnl and sad_count set
+ *
+ * This is a helper for determining the payload size of the baseline block, in
+ * bytes, for e.g. setting the Baseline_ELD_Len field in the ELD header block.
+ */
+static inline int drm_eld_calc_baseline_block_size(const u8 *eld)
+{
+	return DRM_ELD_MONITOR_NAME_STRING - DRM_ELD_HEADER_BLOCK_SIZE +
+		drm_eld_mnl(eld) + drm_eld_sad_count(eld) * 3;
+}
+
+/**
+ * drm_eld_size - Get ELD size in bytes
+ * @eld: pointer to a complete eld memory structure
+ *
+ * The returned value does not include the vendor block. It's vendor specific,
+ * and comprises of the remaining bytes in the ELD memory buffer after
+ * drm_eld_size() bytes of header and baseline block.
+ *
+ * The returned value is guaranteed to be a multiple of 4.
+ */
+static inline int drm_eld_size(const u8 *eld)
+{
+	return DRM_ELD_HEADER_BLOCK_SIZE + eld[DRM_ELD_BASELINE_ELD_LEN] * 4;
+}
+
+/**
+ * drm_eld_get_spk_alloc - Get speaker allocation
+ * @eld: pointer to an ELD memory structure
+ *
+ * The returned value is the speakers mask. User has to use %DRM_ELD_SPEAKER
+ * field definitions to identify speakers.
+ */
+static inline u8 drm_eld_get_spk_alloc(const u8 *eld)
+{
+	return eld[DRM_ELD_SPEAKER] & DRM_ELD_SPEAKER_MASK;
+}
+
+/**
+ * drm_eld_get_conn_type - Get device type hdmi/dp connected
+ * @eld: pointer to an ELD memory structure
+ *
+ * The caller need to use %DRM_ELD_CONN_TYPE_HDMI or %DRM_ELD_CONN_TYPE_DP to
+ * identify the display type connected.
+ */
+static inline u8 drm_eld_get_conn_type(const u8 *eld)
+{
+	return eld[DRM_ELD_SAD_COUNT_CONN_TYPE] & DRM_ELD_CONN_TYPE_MASK;
+}
+
+#endif /* __DRM_ELD_H__ */