linux-kernel - [PATCH 002/003] Attempt to cope with device changes and delayed kobject deallocation

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Message-ID: <555B5380.90601@kynesim.co.uk>
Date:	Tue, 19 May 2015 16:15:12 +0100
From:	Richard Watts <rrw@...esim.co.uk>
To:	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: [PATCH 002/003] Attempt to cope with device changes and delayed kobject
 deallocation

Avoid attempts to use device parents with zero refcounts

Signed-off-by: Richard Watts <rrw@...esim.co.uk>
---
  drivers/base/core.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 21d1303..207fbb2 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -762,7 +762,13 @@ static struct kobject *get_device_parent(struct 
device *dev,
  		spin_lock(&dev->class->p->glue_dirs.list_lock);
  		list_for_each_entry(k, &dev->class->p->glue_dirs.list, entry)
  			if (k->parent == parent_kobj) {
-				kobj = kobject_get(k);
+				/* Be careful: an old parent may still
+				 * be in this list awaiting deletion, despite
+				 * having a refcount of 0. We don't want to
+				 * add it here and then have some other thread
+				 * delete it.
+				 */
+				kobj = kobject_get_unless_zero(k);
  				break;
  			}
  		spin_unlock(&dev->class->p->glue_dirs.list_lock);
-- 
1.9.1

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