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Subject[S390] cio: subchannel evaluation function operates without lock
From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

[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: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

drivers/s390/cio/css.c | 203 +++++++++++++++++++++++++------------------------
1 files changed, 104 insertions(+), 99 deletions(-)

diff -urpN linux-2.6/drivers/s390/cio/css.c linux-2.6-patched/drivers/s390/cio/css.c
--- linux-2.6/drivers/s390/cio/css.c 2006-09-19 12:58:32.000000000 +0200
+++ linux-2.6-patched/drivers/s390/cio/css.c 2006-09-19 12:59:33.000000000 +0200
@@ -182,136 +182,141 @@ get_subchannel_by_schid(struct subchanne
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)
- device_kill_pending_timer(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",
- slow?"slow":"fast");
+ 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;
+ if (disc) {
+ /* Check if paths have become available. */
+ action = REPROBE;
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);
+ /* fall through */
+ case CIO_GONE:
+ /* Prevent unwanted effects when opening lock. */
+ cio_disable_subchannel(sch);
+ device_set_disconnected(sch);
+ /* Ask driver what to do with device. */
+ action = UNREGISTER;
+ if (sch->driver && sch->driver->notify) {
spin_unlock_irqrestore(&sch->lock, flags);
- ret = 0;
- break;
- }
- if (sch->driver && sch->driver->notify &&
- sch->driver->notify(&sch->dev, event)) {
- cio_disable_subchannel(sch);
- device_set_disconnected(sch);
- ret = 0;
- break;
+ 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) {
- css_sch_device_unregister(sch);
- /* 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;
- }
+ /* 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) {
- spin_lock_irqsave(&sch->lock, flags);
+ if (disc)
/* Get device operational again. */
- device_trigger_reprobe(sch);
- spin_unlock_irqrestore(&sch->lock, flags);
- }
- ret = sch ? 0 : css_probe_device(schid);
+ 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);
+
+ /* Probe if necessary. */
+ if (action == UNREGISTER_PROBE)
+ ret = css_probe_device(sch->schid);
+ break;
+ case REPROBE:
+ device_trigger_reprobe(sch);
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;
}

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