From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: pmladek@suse.com, sergey.senozhatsky@gmail.com,
rostedt@goodmis.org, john.ogness@linutronix.de,
akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] printk: fix deadlock when kernel panic
Date: Mon, 8 Feb 2021 15:38:44 +0900 [thread overview]
Message-ID: <YCDcAy39BbPItdGY@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <20210206054124.6743-1-songmuchun@bytedance.com>
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
next prev parent reply other threads:[~2021-02-08 6:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-06 5:41 Muchun Song
2021-02-08 6:38 ` Sergey Senozhatsky [this message]
2021-02-08 8:49 ` [External] " Muchun Song
2021-02-08 13:12 ` Sergey Senozhatsky
2021-02-08 15:40 ` Muchun Song
2021-02-09 8:39 ` Petr Mladek
2021-02-10 2:25 ` Sergey Senozhatsky
2021-02-09 9:19 ` Petr Mladek
2021-02-09 12:20 ` [External] " Muchun Song
2021-02-10 2:16 ` Sergey Senozhatsky
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