linux-kernel - Re: [PATCH v6 2/2] printk: Make printing of spin

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Date:	Mon, 14 Mar 2016 10:37:52 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
	sergey.senozhatsky.work@...il.com, peter@...leysoftware.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org
Subject: Re: [PATCH v6 2/2] printk: Make printing of spin_dump() deferred to
 avoid a deadlock

On (03/11/16 19:37), Byungchul Park wrote:
[..]
> +static void __spin_dump_deferred(raw_spinlock_t *lock, const char *msg)
> +{
> +	printk_func_t s;
> +
> +	s = this_cpu_read(printk_func);
> +	this_cpu_write(printk_func, vprintk_deferred);
> +
> +	/*
> +	 * To change printk_func, it must be in preempt disabled and irq
> +	 * disabled. WARN_ON() should be called after the change because
> +	 * the default printk_func which may be called from WARN_ON()
> +	 * is prohibited in this context.
> +	 */
> +	WARN_ON(!preempt_count() || !irqs_disabled());
> +	__spin_dump(lock, msg);
> +
> +	this_cpu_write(printk_func, s);
> +
> +	printk_pending_output();
> +}
>
> +static void spin_dump(raw_spinlock_t *lock, const char *msg)
> +{
> +	if (unlikely(console_sem_spin_is_held()))
> +		__spin_dump_deferred(lock, msg);
> +	else
> +		__spin_dump(lock, msg);
> +}

so can it be

vprintk_emit()
 __spin_dump_deferred()
  vprintk_deferred()
   vprintk_emit()
    __spin_dump_deferred()
     vprintk_deferred()


or am I getting it wrong?

	-ss