Messages in this thread | | | Date | Mon, 8 Feb 2021 15:38:44 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH v2] printk: fix deadlock when kernel panic |
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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
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