linux-kernel - schedule inside spin_lock

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Message-ID: <20100530145240.GA21559@linux-m68k.org>
Date:	Sun, 30 May 2010 16:52:40 +0200
From:	Richard Zidlicky <rz@...ux-m68k.org>
To:	linux-kernel@...r.kernel.org
Subject: schedule inside spin_lock_irqsave?

Hi,

came across following snippet of code (2.6.34:drivers/media/dvb/siano/smscoreapi.c) and 
since prepare_to_wait is new for me I am wondering if this is can work?

struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t *coredev)
{
	struct smscore_buffer_t *cb = NULL;
	unsigned long flags;

	DEFINE_WAIT(wait);

	spin_lock_irqsave(&coredev->bufferslock, flags);

	/* This function must return a valid buffer, since the buffer list is
	 * finite, we check that there is an available buffer, if not, we wait
	 * until such buffer become available.
	 */

	prepare_to_wait(&coredev->buffer_mng_waitq, &wait, TASK_INTERRUPTIBLE);

	if (list_empty(&coredev->buffers))
		schedule();

	finish_wait(&coredev->buffer_mng_waitq, &wait);

	cb = (struct smscore_buffer_t *) coredev->buffers.next;
	list_del(&cb->entry);

	spin_unlock_irqrestore(&coredev->bufferslock, flags);

	return cb;
}

Regards
Richard
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