From: Huacai Chen <chenhuacai@loongson.cn> mainline inclusion from mainline-v7.2-rc1 commit f2539c56c74691e7a88af6372ba2b48c06ed2fe4 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/16476 CVE: CVE-2026-64073 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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: <stable@vger.kernel.org> Fixes: 91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT") Reviewed-by: Guo Ren <guoren@kernel.org> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> Conflcits: arch/loongarch/kernel/smp.c [ rcu_report_dead() has not renamed to rcutree_report_cpu_dead(). ] Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com> --- arch/loongarch/kernel/smp.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c index 585aeac7fc55..2786e725b3e6 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -14,6 +14,7 @@ #include <linux/init.h> #include <linux/interrupt.h> #include <linux/profile.h> +#include <linux/rcupdate.h> #include <linux/seq_file.h> #include <linux/smp.h> #include <linux/threads.h> @@ -682,9 +683,12 @@ void __init smp_cpus_done(unsigned int max_cpus) static void stop_this_cpu(void *dummy) { - set_cpu_online(smp_processor_id(), false); + int cpu = smp_processor_id(); + + set_cpu_online(cpu, false); calculate_cpu_foreign_map(); local_irq_disable(); + rcu_report_dead(cpu); while (true); } -- 2.34.1