On (21/02/06 13:41), Muchun Song wrote: > We found a deadlock bug on our server when the kernel panic. It can be > described in the following diagram. > > CPU0: CPU1: > panic rcu_dump_cpu_stacks > kdump_nmi_shootdown_cpus nmi_trigger_cpumask_backtrace > register_nmi_handler(crash_nmi_callback) printk_safe_flush > __printk_safe_flush > > raw_spin_lock_irqsave(&read_lock) > // send NMI to other processors > apic_send_IPI_allbutself(NMI_VECTOR) > // NMI interrupt, > dead loop > crash_nmi_callback
At what point does this decrement num_online_cpus()? Any chance that panic CPU can apic_send_IPI_allbutself() and printk_safe_flush_on_panic() before num_online_cpus() becomes 1? > printk_safe_flush_on_panic > printk_safe_flush > __printk_safe_flush > // deadlock > raw_spin_lock_irqsave(&read_lock) -ss