From 90e254f18b8c224460082329dd5c42fd30995c2f Mon Sep 17 00:00:00 2001 From: Huacai Chen Date: Thu, 25 Jun 2026 13:03:49 +0800 Subject: LoongArch: Report dying CPU to RCU in stop_this_cpu() commit f2539c56c74691e7a88af6372ba2b48c06ed2fe4 upstream. This is a port of MIPS commit 9f3f3bdc6d9dac1 ("MIPS: smp: report dying CPU to RCU in stop_this_cpu()"). smp_send_stop() parks all secondary CPUs in stop_this_cpu(). And the function marks the CPU offline for the scheduler via set_cpu_online(false) but never informs RCU, so RCU keeps expecting a quiescent state from CPUs that are now spinning forever with interrupts disabled. As long as nothing waits for an RCU grace period after smp_send_stop() this is harmless, which is why it went unnoticed. However, since commit 91840be8f710370 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT"), irq_work_sync() calls synchronize_rcu() on architectures without an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns false. Any irq_work_sync() issued in the reboot/shutdown/halt path after smp_send_stop() then blocks on a grace period that can never complete, hanging the reboot: WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on ... rcu: INFO: rcu_sched detected stalls on CPUs/tasks: rcu: Offline CPU 1 blocking current GP. rcu: Offline CPU 2 blocking current GP. rcu: Offline CPU 3 blocking current GP. This issue needs some hacks to reproduce, and it was not noticed on LoongArch because arch_irq_work_has_interrupt() usually returns true. Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs and grace periods can still complete. LoongArch shuts down all CPUs here without going through the CPU-hotplug mechanism, so this report is not otherwise issued. Cc: Fixes: 91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT") Reviewed-by: Guo Ren Signed-off-by: Huacai Chen Signed-off-by: Greg Kroah-Hartman --- arch/loongarch/kernel/smp.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c index 46036d98da75..5d6a60294fb2 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -688,6 +688,7 @@ static void stop_this_cpu(void *dummy) set_cpu_online(smp_processor_id(), false); calculate_cpu_foreign_map(); local_irq_disable(); + rcutree_report_cpu_dead(); while (true); } -- cgit v1.2.3