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Date: Fri, 18 May 2018 15:38:20 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
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Subject: Re: [PATCH] printk/nmi: Prevent deadlock when serializing NMI
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 <20180518020705.GB1160@jagdpanzerIV>
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On (05/18/18 11:07), Sergey Senozhatsky wrote:
> 
> if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK) ||
> 	raw_spin_is_locked(&logbuf_lock)
> 
> just to check per-CPU `printk_context' first and only afterwards
> access the global `logbuf_lock'. printk_nmi_enter() happens on
> every CPU, so maybe we can avoid some overhead by checking the
> local per-CPU data first.

Nah, may be it won't. This, probably, would have been the case if we
had continue to call console drivers from printk_safe section [at least].
CPUs don't spend that much time in printk_safe sections.

	-ss