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Commit 564337f3 authored by Peter Oberparleiter's avatar Peter Oberparleiter Committed by Martin Schwidefsky
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[S390] cio: subchannel evaluation function operates without lock 



css_evaluate_subchannel() operates subchannel without lock which can
lead to erratic behavior caused by concurrent device access. Also
split evaluation function to make it more readable.

Signed-off-by: default avatarPeter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 28bdc6f6

drivers/s390/cio/css.c

+104 −99
Original line number Diff line number Diff line
@@ -182,136 +182,141 @@ get_subchannel_by_schid(struct subchannel_id schid) 
	return dev ? to_subchannel(dev) : NULL;

}





static inline int

css_get_subchannel_status(struct subchannel *sch, struct subchannel_id schid)

static inline int css_get_subchannel_status(struct subchannel *sch)

{

	struct schib schib;

	int cc;



	cc = stsch(schid, &schib);

	if (cc)

		return CIO_GONE;

	if (!schib.pmcw.dnv)

	if (stsch(sch->schid, &schib) || !schib.pmcw.dnv)

		return CIO_GONE;

	if (sch && sch->schib.pmcw.dnv &&

	    (schib.pmcw.dev != sch->schib.pmcw.dev))

	if (sch->schib.pmcw.dnv && (schib.pmcw.dev != sch->schib.pmcw.dev))

		return CIO_REVALIDATE;

	if (sch && !sch->lpm)

	if (!sch->lpm)

		return CIO_NO_PATH;

	return CIO_OPER;

}



static int

css_evaluate_subchannel(struct subchannel_id schid, int slow)

static int css_evaluate_known_subchannel(struct subchannel *sch, int slow)

{

	int event, ret, disc;

	struct subchannel *sch;

	unsigned long flags;

	enum { NONE, UNREGISTER, UNREGISTER_PROBE, REPROBE } action;



	sch = get_subchannel_by_schid(schid);

	disc = sch ? device_is_disconnected(sch) : 0;

	spin_lock_irqsave(&sch->lock, flags);

	disc = device_is_disconnected(sch);

	if (disc && slow) {

		if (sch)

			put_device(&sch->dev);

		return 0; /* Already processed. */

		/* Disconnected devices are evaluated directly only.*/

		spin_unlock_irqrestore(&sch->lock, flags);

		return 0;

	}

	/*

	 * We've got a machine check, so running I/O won't get an interrupt.

	 * Kill any pending timers.

	 */

	if (sch)

	/* No interrupt after machine check - kill pending timers. */

	device_kill_pending_timer(sch);

	if (!disc && !slow) {

		if (sch)

			put_device(&sch->dev);

		return -EAGAIN; /* Will be done on the slow path. */

		/* Non-disconnected devices are evaluated on the slow path. */

		spin_unlock_irqrestore(&sch->lock, flags);

		return -EAGAIN;

	}

	event = css_get_subchannel_status(sch, schid);

	event = css_get_subchannel_status(sch);

	CIO_MSG_EVENT(4, "Evaluating schid 0.%x.%04x, event %d, %s, %s path.\n",

		      schid.ssid, schid.sch_no, event,

		      sch?(disc?"disconnected":"normal"):"unknown",

		      sch->schid.ssid, sch->schid.sch_no, event,

		      disc ? "disconnected" : "normal",

		      slow ? "slow" : "fast");

	/* Analyze subchannel status. */

	action = NONE;

	switch (event) {

	case CIO_NO_PATH:

	case CIO_GONE:

		if (!sch) {

			/* Never used this subchannel. Ignore. */

			ret = 0;

			break;

		}

		if (disc && (event == CIO_NO_PATH)) {

			/*

			 * Uargh, hack again. Because we don't get a machine

			 * check on configure on, our path bookkeeping can

			 * be out of date here (it's fine while we only do

			 * logical varying or get chsc machine checks). We

			 * need to force reprobing or we might miss devices

			 * coming operational again. It won't do harm in real

			 * no path situations.

			 */

			spin_lock_irqsave(&sch->lock, flags);

			device_trigger_reprobe(sch);

			spin_unlock_irqrestore(&sch->lock, flags);

			ret = 0;

		if (disc) {

			/* Check if paths have become available. */

			action = REPROBE;

			break;

		}

		if (sch->driver && sch->driver->notify &&

		    sch->driver->notify(&sch->dev, event)) {

		/* fall through */

	case CIO_GONE:

		/* Prevent unwanted effects when opening lock. */

		cio_disable_subchannel(sch);

		device_set_disconnected(sch);

			ret = 0;

			break;

		/* Ask driver what to do with device. */

		action = UNREGISTER;

		if (sch->driver && sch->driver->notify) {

			spin_unlock_irqrestore(&sch->lock, flags);

			ret = sch->driver->notify(&sch->dev, event);

			spin_lock_irqsave(&sch->lock, flags);

			if (ret)

				action = NONE;

		}

		/*

		 * Unregister subchannel.

		 * The device will be killed automatically.

		 */

		cio_disable_subchannel(sch);

		css_sch_device_unregister(sch);

		/* Reset intparm to zeroes. */

		sch->schib.pmcw.intparm = 0;

		cio_modify(sch);

		put_device(&sch->dev);

		ret = 0;

		break;

	case CIO_REVALIDATE:

		/* 

		 * Revalidation machine check. Sick.

		 * We don't notify the driver since we have to throw the device

		 * away in any case.

		 */

		if (!disc) {

		/* Device will be removed, so no notify necessary. */

		if (disc)

			/* Reprobe because immediate unregister might block. */

			action = REPROBE;

		else

			action = UNREGISTER_PROBE;

		break;

	case CIO_OPER:

		if (disc)

			/* Get device operational again. */

			action = REPROBE;

		break;

	}

	/* Perform action. */

	ret = 0;

	switch (action) {

	case UNREGISTER:

	case UNREGISTER_PROBE:

		/* Unregister device (will use subchannel lock). */

		spin_unlock_irqrestore(&sch->lock, flags);

		css_sch_device_unregister(sch);

		spin_lock_irqsave(&sch->lock, flags);



		/* Reset intparm to zeroes. */

		sch->schib.pmcw.intparm = 0;

		cio_modify(sch);

			put_device(&sch->dev);

			ret = css_probe_device(schid);

		} else {

			/*

			 * We can't immediately deregister the disconnected

			 * device since it might block.

			 */

			spin_lock_irqsave(&sch->lock, flags);

			device_trigger_reprobe(sch);

			spin_unlock_irqrestore(&sch->lock, flags);

			ret = 0;

		}



		/* Probe if necessary. */

		if (action == UNREGISTER_PROBE)

			ret = css_probe_device(sch->schid);

		break;

	case CIO_OPER:

		if (disc) {

			spin_lock_irqsave(&sch->lock, flags);

			/* Get device operational again. */

	case REPROBE:

		device_trigger_reprobe(sch);

			spin_unlock_irqrestore(&sch->lock, flags);

		}

		ret = sch ? 0 : css_probe_device(schid);

		break;

	default:

		BUG();

		ret = 0;

		break;

	}

	spin_unlock_irqrestore(&sch->lock, flags);



	return ret;

}



static int css_evaluate_new_subchannel(struct subchannel_id schid, int slow)

{

	struct schib schib;



	if (!slow) {

		/* Will be done on the slow path. */

		return -EAGAIN;

	}

	if (stsch(schid, &schib) || !schib.pmcw.dnv) {

		/* Unusable - ignore. */

		return 0;

	}

	CIO_MSG_EVENT(4, "Evaluating schid 0.%x.%04x, event %d, unknown, "

			 "slow path.\n", schid.ssid, schid.sch_no, CIO_OPER);



	return css_probe_device(schid);

}



static int css_evaluate_subchannel(struct subchannel_id schid, int slow)

{

	struct subchannel *sch;

	int ret;



	sch = get_subchannel_by_schid(schid);

	if (sch) {

		ret = css_evaluate_known_subchannel(sch, slow);

		put_device(&sch->dev);

	} else

		ret = css_evaluate_new_subchannel(schid, slow);



	return ret;

}