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// SPDX-License-Identifier: GPL-2.0
/*
* A cid-form scheduler checking the cmask cid-form ops.enable() receives: the
* header, every cid bit against p->cpus_ptr, and that set_cmask() follows with
* the same mask before set_weight() and before the task first becomes runnable,
* and never runs before enable().
*
* Copyright (c) 2026 Tejun Heo <tj@kernel.org>
*/
#include <scx/common.bpf.h>
char _license[] SEC("license") = "GPL";
struct {
__uint(type, BPF_MAP_TYPE_ARENA);
__uint(map_flags, BPF_F_MMAPABLE);
__uint(max_entries, 1 << 16);
} arena SEC(".maps");
struct task_ctx {
u64 enable_fp; /* fingerprint of the mask enable() received */
bool enabled;
bool pending; /* enable() ran, the initial set_cmask() hasn't */
};
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
__type(key, int);
__type(value, struct task_ctx);
} task_ctx_stor SEC(".maps");
/* details of a cid bit mismatch, filled by check_mask() */
struct mask_mismatch {
s32 cid;
bool want;
bool got;
};
u64 nr_enable, nr_initial_set_cmask, nr_set_cmask, nr_set_weight;
UEI_DEFINE(uei);
static struct task_ctx *lookup_task_ctx(struct task_struct *p)
{
struct task_ctx *tctx;
tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
if (!tctx)
scx_bpf_error("task_ctx lookup failed for %s[%d]", p->comm, p->pid);
return tctx;
}
/*
* Verify @m's header and every cid bit against @p's cpumask and fingerprint the
* bits into @fp. Return 0 on success, -EINVAL on a bad header, -ENOENT on a cid
* without a cpu and -EIO on a bit mismatch with the details in @mm.
*/
static int check_mask(struct task_struct *p, const struct scx_cmask __arena *m, u64 *fp,
struct mask_mismatch *mm)
{
u32 nr_cids = scx_bpf_nr_cids();
u64 h = 0;
s32 cid;
if (m->base || m->nr_cids != nr_cids || m->alloc_words != CMASK_NR_WORDS(nr_cids))
return -EINVAL;
bpf_for(cid, 0, nr_cids) {
bool want, got;
s32 cpu;
cpu = scx_bpf_cid_to_cpu(cid);
if (cpu < 0)
return -ENOENT;
want = bpf_cpumask_test_cpu(cpu, p->cpus_ptr);
got = cmask_test(cid, m);
if (want != got) {
mm->cid = cid;
mm->want = want;
mm->got = got;
return -EIO;
}
h = h * 31 + got;
}
*fp = h;
return 0;
}
s32 BPF_STRUCT_OPS_SLEEPABLE(enable_cmask_init_task, struct task_struct *p,
struct scx_init_task_args *args)
{
if (!bpf_task_storage_get(&task_ctx_stor, p, 0, BPF_LOCAL_STORAGE_GET_F_CREATE))
return -ENOMEM;
return 0;
}
void BPF_STRUCT_OPS(enable_cmask_enable, struct task_struct *p, struct scx_enable_args *args)
{
struct scx_cmask __arena *m = (struct scx_cmask __arena *)args->cmask_arena_addr;
struct mask_mismatch mm = {};
struct task_ctx *tctx;
int ret;
asm volatile("" :: "r"(&arena));
tctx = lookup_task_ctx(p);
if (!tctx)
return;
__sync_fetch_and_add(&nr_enable, 1);
if (tctx->enabled || tctx->pending) {
scx_bpf_error("enable: %s[%d] enabled twice", p->comm, p->pid);
return;
}
ret = check_mask(p, m, &tctx->enable_fp, &mm);
if (ret) {
scx_bpf_error("enable: %s[%d] cmask check failed %d cid=%d want=%d got=%d",
p->comm, p->pid, ret, mm.cid, mm.want, mm.got);
return;
}
tctx->enabled = true;
tctx->pending = true;
}
void BPF_STRUCT_OPS(enable_cmask_set_cmask, struct task_struct *p,
struct scx_cmask __arena *m)
{
struct mask_mismatch mm = {};
struct task_ctx *tctx;
u64 fp;
int ret;
asm volatile("" :: "r"(&arena));
tctx = lookup_task_ctx(p);
if (!tctx)
return;
__sync_fetch_and_add(&nr_set_cmask, 1);
if (!tctx->enabled) {
scx_bpf_error("set_cmask: %s[%d] not enabled", p->comm, p->pid);
return;
}
ret = check_mask(p, m, &fp, &mm);
if (ret) {
scx_bpf_error("set_cmask: %s[%d] cmask check failed %d cid=%d want=%d got=%d",
p->comm, p->pid, ret, mm.cid, mm.want, mm.got);
return;
}
if (tctx->pending) {
if (fp != tctx->enable_fp) {
scx_bpf_error("set_cmask: %s[%d] initial mask differs from enable()",
p->comm, p->pid);
return;
}
tctx->pending = false;
__sync_fetch_and_add(&nr_initial_set_cmask, 1);
}
}
void BPF_STRUCT_OPS(enable_cmask_set_weight, struct task_struct *p, u32 weight)
{
struct task_ctx *tctx;
tctx = lookup_task_ctx(p);
if (!tctx)
return;
__sync_fetch_and_add(&nr_set_weight, 1);
if (tctx->pending)
scx_bpf_error("set_weight: %s[%d] before the initial set_cmask()", p->comm,
p->pid);
}
void BPF_STRUCT_OPS(enable_cmask_runnable, struct task_struct *p, u64 enq_flags)
{
struct task_ctx *tctx;
tctx = lookup_task_ctx(p);
if (!tctx)
return;
if (tctx->pending)
scx_bpf_error("runnable: %s[%d] before the initial set_cmask()", p->comm,
p->pid);
}
void BPF_STRUCT_OPS(enable_cmask_disable, struct task_struct *p)
{
struct task_ctx *tctx;
tctx = lookup_task_ctx(p);
if (!tctx)
return;
tctx->enabled = false;
tctx->pending = false;
}
void BPF_STRUCT_OPS(enable_cmask_exit, struct scx_exit_info *ei)
{
UEI_RECORD(uei, ei);
}
SCX_OPS_CID_DEFINE(enable_cmask_ops,
.init_task = (void *)enable_cmask_init_task,
.enable = (void *)enable_cmask_enable,
.set_cmask = (void *)enable_cmask_set_cmask,
.set_weight = (void *)enable_cmask_set_weight,
.runnable = (void *)enable_cmask_runnable,
.disable = (void *)enable_cmask_disable,
.exit = (void *)enable_cmask_exit,
.flags = SCX_OPS_SWITCH_PARTIAL,
.name = "enable_cmask");
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