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/uapi/asm-generic/ipcbuf.h | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) create mode 100644 include/uapi/asm-generic/ipcbuf.h (limited to 'include/uapi/asm-generic/ipcbuf.h') diff --git a/include/uapi/asm-generic/ipcbuf.h b/include/uapi/asm-generic/ipcbuf.h new file mode 100644 index 000000000..41a01b494 --- /dev/null +++ b/include/uapi/asm-generic/ipcbuf.h @@ -0,0 +1,37 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef __ASM_GENERIC_IPCBUF_H +#define __ASM_GENERIC_IPCBUF_H + +#include + +/* + * The generic ipc64_perm structure: + * Note extra padding because this structure is passed back and forth + * between kernel and user space. + * + * ipc64_perm was originally meant to be architecture specific, but + * everyone just ended up making identical copies without specific + * optimizations, so we may just as well all use the same one. + * + * Pad space is left for: + * - 32-bit mode_t on architectures that only had 16 bit + * - 32-bit seq + * - 2 miscellaneous 32-bit values + */ + +struct ipc64_perm { + __kernel_key_t key; + __kernel_uid32_t uid; + __kernel_gid32_t gid; + __kernel_uid32_t cuid; + __kernel_gid32_t cgid; + __kernel_mode_t mode; + /* pad if mode_t is u16: */ + unsigned char __pad1[4 - sizeof(__kernel_mode_t)]; + unsigned short seq; + unsigned short __pad2; + __kernel_ulong_t __unused1; + __kernel_ulong_t __unused2; +}; + +#endif /* __ASM_GENERIC_IPCBUF_H */ -- cgit v1.3.1