monitor_timerfn(), lowpri_timerfn() and round_robin_timerfn() ignore
bpf_timer_start()'s return value: a failed re-arm silently stops the
periodic heartbeat, starving every task parked in LOWPRI_DSQ (lowpri)
or freezing cid rotation (round-robin).  Check the returns and raise
scx_bpf_error(), matching the init paths.

Signed-off-by: Wanwu Li <liwanwu@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>

fcg_cgroup_move() lost the signed vtime offset across cgroup
migration in the mechanical conversion to time helpers:
time_delta() clamps negative deltas to 0, so a queued task (whose
dsq_vtime is normally behind the source frontier) loses its
accumulated vtime credit and lands exactly at the destination
frontier instead of keeping its relative position.  Restore the
wrapping signed subtraction.

Fixes: 62addc6dbf36 ("sched_ext: Use time helpers in BPF schedulers")
Signed-off-by: Wanwu Li <liwanwu@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>

central_timerfn() re-arms the timer with a hardcoded
BPF_F_TIMER_CPU_PIN flag and ignores the return value, defeating
start_central_timer()'s -EINVAL fallback for kernels without the flag
(<6.7): on such kernels the first tick kills the timer permanently
with no diagnostic.  Honor timer_pinned and check the return like
the initial arm does.

Fixes: 22a920209ab6 ("sched_ext: Implement tickless support")
Signed-off-by: Wanwu Li <liwanwu@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>

Sync common.bpf.h, compat.bpf.h and compat.h with the scx repo, which
accumulated the following:

- __COMPAT_read_enum() can now recover 64-bit scx enum values from kernel
  BTF generated without BTF_KIND_ENUM64 support (pahole < 1.24 or
  --skip_encoding_btf_enum64, e.g. COS/GKE kernels), substituting values
  from the build-time vmlinux.h cross-checked against the low 32 bits the
  kernel does provide.

- is_migration_disabled() no longer assumes the BPF prolog always disables
  migration. Since 8e4f0b1ebcf2 ("bpf: use rcu_read_lock_dont_migrate() for
  trampoline.c") the prolog only does so under CONFIG_PREEMPT_RCU, so the
  old current-task test under-reported on v6.18+ !PREEMPT_RCU kernels. A
  runtime probe on bpf_scx_reg() handles older kernels with backported
  trampoline behavior.

- __COMPAT_scx_bpf_dsq_peek() is gated behind kernel v7.1 where 2f2ea7709266
  ("sched_ext: Use dsq->first_task instead of list_empty() in
  dispatch_enqueue() FIFO-tail") fixed the kfunc spuriously returning NULL
  on non-empty FIFO DSQs, and the new
  scx_bpf_reenqueue_local_from_anywhere() provides a callable-from-anywhere
  reenqueue which prefers the generic scx_bpf_dsq_reenq(). Both were first
  posted by Gavin Guo and Changwoo Min and are picked up here with the
  review feedback folded in.

- __COMPAT_scx_bpf_cpu_curr() and the scx_bpf_cpu_rq() declaration are
  restored. Schedulers built from these headers still run on pre-v6.18
  kernels where scx_bpf_cpu_curr() does not resolve and the scx_bpf_cpu_rq()
  fallback still exists.

- scx_clock_task() and scx_clock_pelt() document their stale-read behavior
  for remote idle CPUs under NO_HZ_IDLE.

Link: https://lore.kernel.org/all/20260817143126.562923-1-changwoo@igalia.com
Signed-off-by: Tejun Heo <tj@kernel.org>

Regenerate enum_defs.autogen.h against the current tree, picking up the
dispatch verdict enums and dropping the marker for the removed
SCX_RQ_IN_BALANCE. Add enums_abi.autogen.h, a table of 64-bit scx enumerator
values generated from vmlinux.h, used as the substitution source when the
running kernel's BTF truncates 64-bit enum values to 32 bits.

Signed-off-by: Tejun Heo <tj@kernel.org>

Pull to receive the __arena argument conversion:

 67f1f4a48c24 ("sched_ext: Pass kernel arena pointers to ops_cid callbacks")
 a8dc810968af ("sched_ext: Convert sub-cap kfuncs to __arena cmask arguments")
 a05c5b5cb5cf ("sched_ext: Convert scx_bpf_cid_override() to __arena array arguments")

along with the bpf-next branch carrying the __arena argument support they
depend on.

Conflict in kernel/sched/ext/ext.c between:

 c384ab8a0b13 ("sched_ext: Move the config-off sub-cap kfunc stubs into sub.c")

and:

 a8dc810968af ("sched_ext: Convert sub-cap kfuncs to __arena cmask arguments")

which updated the stubs in their old ext.c location. Resolved by keeping
ext.c without the stubs and applying the prototype conversion to the
relocated stubs in sub.c.

Signed-off-by: Tejun Heo <tj@kernel.org>

With sub-schedulers, tasks of different schedulers routinely share rqs and
SMT siblings, but scx_prio_less() consults ops.core_sched_before() only when
both tasks belong to the same scheduler. Every pair spanning two schedulers
falls back to the default ordering, so no scheduler can express ordering
across a scheduler boundary, including a root over its sub-schedulers'
tasks.

Order a pair spanning schedulers by the nearest common ancestor that
implements ops.core_sched_before(): both tasks are in its subtree, making
this the one op where a scheduler is called on tasks it delegated to its
sub-schedulers and may not be scheduling anymore. Same-scheduler pairs keep
using the owning scheduler's op so a parent never orders inside a subtree it
delegated. The op is skipped when the deciding scheduler is bypassing on
either task's CPU.

Update scx_qmap to fall back to the kernel's default ordering when handed a
delegated task it has no task_ctx for.

Signed-off-by: Tejun Heo <tj@kernel.org>

scx_prio_less() implements prio_less() semantics - %true means that @a is
the lower priority and should run after @b. ops.core_sched_before() is
documented to return %true when @a should run before @b. scx_prio_less()
returns the op's value as-is, inverting the documented semantics at runtime.

Call the op with the arguments swapped.

scx_qmap followed the wiring instead of the documentation and returned %true
for the younger task, so the two inversions canceled out and it behaved as
intended. Flip its comparison to match. scx_qmap is likely the only current
user in or out of the kernel tree. Any scheduler written the same way needs
the same flip, while schedulers following the documentation are fixed by
this change.

Fixes: 7b0888b7cc19 ("sched_ext: Implement core-sched support")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Tejun Heo <tj@kernel.org>

sched_class->balance() is gone from sched_ext and what balance_one() does is
run dispatch to produce something pickable. Update the balance-era names to
dispatch terms:

- balance_one() -> dispatch_one()
- SCX_RQ_IN_BALANCE -> SCX_RQ_IN_DISPATCH

No BPF scheduler reads the flag. The enum autogen headers gain the new name
with the old entry retained like other removed enumerators, zero-filling at
load time. No functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>

fcg_dispatch() true-ups the current cgroup's cvtime when its slice
expires or its DSQ runs empty while the slice is still active:

	__sync_fetch_and_add(&cgc->cvtime_delta,
			     (cpuc->cur_at + cgrp_slice_ns - now) *
			     FCG_HWEIGHT_ONE / (cgc->hweight ?: 1));

The true-up should be actual minus charged: on CNS_EXPIRE, the overrun
(now - cur_at - cgrp_slice_ns) should be added; on CNS_EMPTY, the
unused portion of the slice should be subtracted. The expression above
has the sign inverted, and in the CNS_EXPIRE case now is already past
cur_at + cgrp_slice_ns, so the u64 subtraction wraps. The
multiplication preserves the two's complement encoding but the
unsigned division by hweight destroys it, adding roughly 2^64/hweight
per expiry instead of a small correction.

Under saturation the hweight budget clamp in cgrp_cap_budget() masks
most of the garbage, so the weight distribution barely moves, but the
accounting is broken all the same. Compute the delta as a signed value
and use fetch_and_add()/fetch_and_sub() so that the dividends stay
positive, as BPF division is unsigned.

Instrumented the true-up and ran a saturated three-leaf cgroup tree on
a 4-CPU VM: without the fix, each expiry added ~5e15 (2^64/hweight
territory) to cvtime_delta; with it, the corrections are back to
slice scale, with the overrun added and the unused portion subtracted.

Fixes: a4103eacc2ab ("sched_ext: Add a cgroup scheduler which uses flattened hierarchy")
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Signed-off-by: Tejun Heo <tj@kernel.org>