linux-kernel - Re: recursion handling: Re: [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog

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Date:   Sat, 5 Dec 2020 18:41:05 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: recursion handling: Re: [PATCH next v2 3/3] printk: remove
 logbuf_lock, add syslog_lock

On (20/12/04 17:10), Petr Mladek wrote:
> 
> One reason is the use of per-cpu variables. Alternative solution would
> be to store printk_context into task_struct.

We can keep per-CPU, disable preemption and have counters for
every context (task, soft/hard irq, NMI). Shouldn't be a problem

	vprintk_emit()
	{
		preempt_disable()
		vprintk_store()
		preempt_enable()

		preempt_disable()
		console_unlock()
		preempt_enable()
	}

vprintk_store() is a small fraction of console_unlock() time wise.

	-ss