linux-kernel - Re: 2.6.21-rc suspend regression: sysfs deadlock

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Date:	Tue, 13 Mar 2007 19:42:04 +0100
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Hugh Dickins <hugh@...itas.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Oliver Neukum <oneukum@...e.de>,
	Maneesh Soni <maneesh@...ibm.com>, <gregkh@...e.de>,
	Richard Purdie <rpurdie@...ys.net>,
	James Bottomley <James.Bottomley@...elEye.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc suspend regression: sysfs deadlock

On Tue, 13 Mar 2007 11:00:21 -0400 (EDT),
Alan Stern <stern@...land.harvard.edu> wrote:

> The consensus is that we would be better off keeping Oliver's original 
> patch without your silly change, and instead fixing the particular method 
> call that deadlocked.

Another call that deadlocked with Oliver's patch is ungroup for s390
ccwgroup devices. It can be made to work again with a similar patch.

Signed-off-by: Cornelia Huck <cornelia.huck@...ibm.com>

---
 drivers/s390/cio/ccwgroup.c |   35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

--- linux-2.6.orig/drivers/s390/cio/ccwgroup.c
+++ linux-2.6/drivers/s390/cio/ccwgroup.c
@@ -67,22 +67,49 @@ __ccwgroup_remove_symlinks(struct ccwgro
 	
 }
 
+struct ccwgroup_work_struct {
+	struct ccwgroup_device *gdev;
+	struct work_struct work;
+};
+
+static void ccwgroup_ungroup_work(struct work_struct *work)
+{
+	struct ccwgroup_work_struct *ungroup_work
+		= container_of(work, struct ccwgroup_work_struct, work);
+
+	__ccwgroup_remove_symlinks(ungroup_work->gdev);
+	device_unregister(&ungroup_work->gdev->dev);
+	put_device(&ungroup_work->gdev->dev);
+	kfree(ungroup_work);
+}
+
 /*
  * Provide an 'ungroup' attribute so the user can remove group devices no
  * longer needed or accidentially created. Saves memory :)
+ * Note that we cannot unregister the device from one of its attribute
+ * methods, so we have to delay it.
  */
-static ssize_t
-ccwgroup_ungroup_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
+static ssize_t ccwgroup_ungroup_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
 {
 	struct ccwgroup_device *gdev;
+	struct ccwgroup_work_struct *ungroup_work;
 
 	gdev = to_ccwgroupdev(dev);
 
 	if (gdev->state != CCWGROUP_OFFLINE)
 		return -EINVAL;
 
-	__ccwgroup_remove_symlinks(gdev);
-	device_unregister(dev);
+	ungroup_work = kmalloc(sizeof(*ungroup_work), GFP_KERNEL);
+	if (!ungroup_work)
+		return -ENOMEM;
+	ungroup_work->gdev = gdev;
+	INIT_WORK(&ungroup_work->work, ccwgroup_ungroup_work);
+	if (!get_device(&gdev->dev))
+		kfree(ungroup_work);
+	else
+		schedule_work(&ungroup_work->work);
 
 	return count;
 }
-
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