On Mon, Feb 8, 2021 at 2:38 PM Sergey Senozhatsky <sergey.senozhat...@gmail.com> wrote: > > 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?
I took a closer look at the code. IIUC, It seems that there is no point which decreases num_online_cpus. > > > printk_safe_flush_on_panic > > printk_safe_flush > > __printk_safe_flush > > // deadlock > > raw_spin_lock_irqsave(&read_lock) > > -ss
