From a9e3760b0838299649c0d57cca44daaf40ba3c33 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 14 Sep 2026 22:12:34 -1000 Subject: sched_ext: Maintain an online cid mask in the scheduler arena Schedulers on the default cid mapping treat [0, nr_online_cids) as the online set and restart on hotplug. Schedulers that install their own mapping with scx_bpf_cid_override() have no way to learn which cids are online: the count no longer identifies members and the CPU-form cpumask is unusable from cid programs. This is an obvious hole in the cid API. Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's arena, allocated alongside the per-CPU scratch masks and populated after the cid mapping is finalized and before ops.init(), for child schedulers too. The pointer stays valid through ops.exit() with no reference to take. It is the arena offset as a void pointer, the same form struct_ops arena arguments arrive in. The verifier types the void return as a scalar for the program's arena cast. The mask follows the SCX hotplug notifications: seeded from cpu_active_mask and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask only inside a hotplug transition. Updates walk the scheduler list under the lock that also serializes unlinking. Reads are live, not atomic snapshots. Root initialization excludes hotplug. v2: Reworded the getter kerneldoc (Andrea Righi). Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- include/asm-generic/atomic64.h | 75 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 include/asm-generic/atomic64.h (limited to 'include/asm-generic/atomic64.h') diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h new file mode 100644 index 000000000..f22ccfc0d --- /dev/null +++ b/include/asm-generic/atomic64.h @@ -0,0 +1,75 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Generic implementation of 64-bit atomics using spinlocks, + * useful on processors that don't have 64-bit atomic instructions. + * + * Copyright © 2009 Paul Mackerras, IBM Corp. + */ +#ifndef _ASM_GENERIC_ATOMIC64_H +#define _ASM_GENERIC_ATOMIC64_H +#include + +typedef struct { + s64 __aligned(sizeof(s64)) counter; +} atomic64_t; + +#define ATOMIC64_INIT(i) { (i) } + +extern s64 generic_atomic64_read(const atomic64_t *v); +extern void generic_atomic64_set(atomic64_t *v, s64 i); + +#define ATOMIC64_OP(op) \ +extern void generic_atomic64_##op(s64 a, atomic64_t *v); + +#define ATOMIC64_OP_RETURN(op) \ +extern s64 generic_atomic64_##op##_return(s64 a, atomic64_t *v); + +#define ATOMIC64_FETCH_OP(op) \ +extern s64 generic_atomic64_fetch_##op(s64 a, atomic64_t *v); + +#define ATOMIC64_OPS(op) ATOMIC64_OP(op) ATOMIC64_OP_RETURN(op) ATOMIC64_FETCH_OP(op) + +ATOMIC64_OPS(add) +ATOMIC64_OPS(sub) + +#undef ATOMIC64_OPS +#define ATOMIC64_OPS(op) ATOMIC64_OP(op) ATOMIC64_FETCH_OP(op) + +ATOMIC64_OPS(and) +ATOMIC64_OPS(or) +ATOMIC64_OPS(xor) + +#undef ATOMIC64_OPS +#undef ATOMIC64_FETCH_OP +#undef ATOMIC64_OP_RETURN +#undef ATOMIC64_OP + +extern s64 generic_atomic64_dec_if_positive(atomic64_t *v); +extern s64 generic_atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n); +extern s64 generic_atomic64_xchg(atomic64_t *v, s64 new); +extern s64 generic_atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u); + +#define arch_atomic64_read generic_atomic64_read +#define arch_atomic64_set generic_atomic64_set +#define arch_atomic64_set_release generic_atomic64_set + +#define arch_atomic64_add generic_atomic64_add +#define arch_atomic64_add_return generic_atomic64_add_return +#define arch_atomic64_fetch_add generic_atomic64_fetch_add +#define arch_atomic64_sub generic_atomic64_sub +#define arch_atomic64_sub_return generic_atomic64_sub_return +#define arch_atomic64_fetch_sub generic_atomic64_fetch_sub + +#define arch_atomic64_and generic_atomic64_and +#define arch_atomic64_fetch_and generic_atomic64_fetch_and +#define arch_atomic64_or generic_atomic64_or +#define arch_atomic64_fetch_or generic_atomic64_fetch_or +#define arch_atomic64_xor generic_atomic64_xor +#define arch_atomic64_fetch_xor generic_atomic64_fetch_xor + +#define arch_atomic64_dec_if_positive generic_atomic64_dec_if_positive +#define arch_atomic64_cmpxchg generic_atomic64_cmpxchg +#define arch_atomic64_xchg generic_atomic64_xchg +#define arch_atomic64_fetch_add_unless generic_atomic64_fetch_add_unless + +#endif /* _ASM_GENERIC_ATOMIC64_H */ -- cgit v1.3.1