Patch "s390/cio: allow to reset channel measurement block" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    s390/cio: allow to reset channel measurement block

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     s390-cio-allow-to-reset-channel-measurement-block.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 0f5d050ceaa31b2229102211d60c149f920df3aa Mon Sep 17 00:00:00 2001
From: Sebastian Ott <sebott@linux.vnet.ibm.com>
Date: Tue, 12 Jul 2016 19:57:57 +0200
Subject: s390/cio: allow to reset channel measurement block

From: Sebastian Ott <sebott@linux.vnet.ibm.com>

commit 0f5d050ceaa31b2229102211d60c149f920df3aa upstream.

Prior to commit 1bc6664bdfb949bc69a08113801e7d6acbf6bc3f a call to
enable_cmf for a device for which channel measurement was already
enabled resulted in a reset of the measurement data.

What looked like bugs at the time (a 2nd allocation was triggered
but failed, reset was called regardless of previous failures, and
errors have not been reported to userspace) was actually something
at least one userspace tool depended on. Restore that behavior in
a sane way.

Fixes: 1bc6664bdfb ("s390/cio: use device_lock during cmb activation")
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/s390/cio/cmf.c |   29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

--- a/drivers/s390/cio/cmf.c
+++ b/drivers/s390/cio/cmf.c
@@ -753,6 +753,17 @@ static void reset_cmb(struct ccw_device
 	cmf_generic_reset(cdev);
 }
 
+static int cmf_enabled(struct ccw_device *cdev)
+{
+	int enabled;
+
+	spin_lock_irq(cdev->ccwlock);
+	enabled = !!cdev->private->cmb;
+	spin_unlock_irq(cdev->ccwlock);
+
+	return enabled;
+}
+
 static struct attribute_group cmf_attr_group;
 
 static struct cmb_operations cmbops_basic = {
@@ -1153,13 +1164,8 @@ static ssize_t cmb_enable_show(struct de
 			       char *buf)
 {
 	struct ccw_device *cdev = to_ccwdev(dev);
-	int enabled;
 
-	spin_lock_irq(cdev->ccwlock);
-	enabled = !!cdev->private->cmb;
-	spin_unlock_irq(cdev->ccwlock);
-
-	return sprintf(buf, "%d\n", enabled);
+	return sprintf(buf, "%d\n", cmf_enabled(cdev));
 }
 
 static ssize_t cmb_enable_store(struct device *dev,
@@ -1199,15 +1205,20 @@ int ccw_set_cmf(struct ccw_device *cdev,
  *  @cdev:	The ccw device to be enabled
  *
  *  Returns %0 for success or a negative error value.
- *
+ *  Note: If this is called on a device for which channel measurement is already
+ *	  enabled a reset of the measurement data is triggered.
  *  Context:
  *    non-atomic
  */
 int enable_cmf(struct ccw_device *cdev)
 {
-	int ret;
+	int ret = 0;
 
 	device_lock(&cdev->dev);
+	if (cmf_enabled(cdev)) {
+		cmbops->reset(cdev);
+		goto out_unlock;
+	}
 	get_device(&cdev->dev);
 	ret = cmbops->alloc(cdev);
 	if (ret)
@@ -1226,7 +1237,7 @@ int enable_cmf(struct ccw_device *cdev)
 out:
 	if (ret)
 		put_device(&cdev->dev);
-
+out_unlock:
 	device_unlock(&cdev->dev);
 	return ret;
 }


Patches currently in stable-queue which might be from sebott@linux.vnet.ibm.com are

queue-4.4/s390-cio-allow-to-reset-channel-measurement-block.patch