From: Andrea Righi Date: Wed, 13 May 2026 11:24:38 +0000 (+0200) Subject: sched_ext: Use HK_TYPE_DOMAIN_BOOT to detect isolcpus= domain isolation X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6ae315d37924435516d697ea7dde0b799a5928e0;p=thirdparty%2Fkernel%2Flinux.git sched_ext: Use HK_TYPE_DOMAIN_BOOT to detect isolcpus= domain isolation scx_enable() refuses to attach a BPF scheduler when isolcpus=domain is in effect by comparing housekeeping_cpumask(HK_TYPE_DOMAIN) against cpu_possible_mask. Since commit 27c3a5967f05 ("sched/isolation: Convert housekeeping cpumasks to rcu pointers"), HK_TYPE_DOMAIN's cpumask is RCU protected and dereferencing it requires either RCU read lock, the cpu_hotplug write lock, or the cpuset lock; scx_enable() holds none of these, so booting with isolcpus=domain and attaching any BPF scheduler triggers the following lockdep splat: ============================= WARNING: suspicious RCU usage ----------------------------- kernel/sched/isolation.c:60 suspicious rcu_dereference_check() usage! 1 lock held by scx_flash/281: #0: ffffffff8379fce0 (update_mutex){+.+.}-{4:4}, at: bpf_struct_ops_link_create+0x134/0x1c0 Call Trace: dump_stack_lvl+0x6f/0xb0 lockdep_rcu_suspicious.cold+0x37/0x70 housekeeping_cpumask+0xcd/0xe0 scx_enable.isra.0+0x17/0x120 bpf_scx_reg+0x5e/0x80 bpf_struct_ops_link_create+0x151/0x1c0 __sys_bpf+0x1e4b/0x33c0 __x64_sys_bpf+0x21/0x30 do_syscall_64+0x117/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f In addition, commit 03ff73510169 ("cpuset: Update HK_TYPE_DOMAIN cpumask from cpuset") made HK_TYPE_DOMAIN include cpuset isolated partitions as well, which means the current check also rejects BPF schedulers when a cpuset partition is active. That contradicts the original intent of commit 9f391f94a173 ("sched_ext: Disallow loading BPF scheduler if isolcpus= domain isolation is in effect"), which explicitly noted that cpuset partitions are honored through per-task cpumasks and should not be rejected. Switch to housekeeping_enabled(HK_TYPE_DOMAIN_BOOT), which reads only the housekeeping flag bit (no RCU dereference) and reflects exactly the boot-time isolcpus= configuration that the error message refers to. Fixes: 27c3a5967f05 ("sched/isolation: Convert housekeeping cpumasks to rcu pointers") Cc: stable@vger.kernel.org # v7.0+ Signed-off-by: Andrea Righi Signed-off-by: Tejun Heo Acked-by: Frederic Weisbecker --- diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 23f7b3f63b09..a6d0a93d8174 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -7415,8 +7415,7 @@ static s32 scx_enable(struct sched_ext_ops *ops, struct bpf_link *link) static DEFINE_MUTEX(helper_mutex); struct scx_enable_cmd cmd; - if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN), - cpu_possible_mask)) { + if (housekeeping_enabled(HK_TYPE_DOMAIN_BOOT)) { pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation\n"); return -EINVAL; }