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Date: Mon, 14 Mar 2016 10:37:52 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-kernel@vger.kernel.org,
        akinobu.mita@gmail.com, jack@suse.cz,
        sergey.senozhatsky.work@gmail.com, peter@hurleysoftware.com,
        tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org
Subject: Re: [PATCH v6 2/2] printk: Make printing of spin_dump() deferred to
 avoid a deadlock
Message-ID: <20160314013752.GB8074@swordfish>
References: <1457692627-14076-1-git-send-email-byungchul.park@lge.com>
 <1457692627-14076-3-git-send-email-byungchul.park@lge.com>
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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