On Wed, Aug 10, 2005 at 04:26:51PM +1000, Keith Owens wrote:
> FYI, the intermittent free after use in sysfs is still there in
> 2.6.13-rc6.
>
The race condition is known here. It is some thing in the upper layer.
In this case "driver/base/class.c" which frees the kobject's attributes
even if there are live references to kobject.
open sysfs file unregister class device
sysfs_open_file() class_device_del()
-> takes a ref on kobject -> kfree attribute struct
-> accesses attributes -> kobject_del()
-> kref_put()
close sysfs file
sysfs_release()
-> acesses attributes using s_element
-> drops ref to kobject
Solution could be either we have reference counting for attributes also
or keep attributes alive till the last reference to the kobject. Both these
needs changes in the driver core.
Greg, will the following patch make sense? This postpones the kfree() of
devt_attr till class_dev_release() is called.
Please check this patch out, if this helps or not.
Thanks
Maneesh
o following patch moves the code to free devt_attr from class_device_del()
to class_dev_release() which is called after the last reference to the
corresponding kobject() is gone. This allows to keep the devt_attr
alive while the corresponding sysfs file is open.
Signed-off-by: Maneesh Soni <[email protected]>
---
linux-2.6.13-rc6-maneesh/drivers/base/class.c | 14 +++++++++-----
1 files changed, 9 insertions(+), 5 deletions(-)
diff -puN drivers/base/class.c~fix-class-attributes-race drivers/base/class.c
--- linux-2.6.13-rc6/drivers/base/class.c~fix-class-attributes-race 2005-08-10 12:35:06.154386456 +0530
+++ linux-2.6.13-rc6-maneesh/drivers/base/class.c 2005-08-10 14:27:12.903765112 +0530
@@ -299,6 +299,11 @@ static void class_dev_release(struct kob
pr_debug("device class '%s': release.\n", cd->class_id);
+ if (cd->devt_attr) {
+ kfree(cd->devt_attr);
+ cd->devt_attr = NULL;
+ }
+
if (cls->release)
cls->release(cd);
else {
@@ -591,11 +596,10 @@ void class_device_del(struct class_devic
if (class_dev->dev)
sysfs_remove_link(&class_dev->kobj, "device");
- if (class_dev->devt_attr) {
- class_device_remove_file(class_dev, class_dev->devt_attr);
- kfree(class_dev->devt_attr);
- class_dev->devt_attr = NULL;
- }
+
+ if (class_dev->devt_attr)
+ class_device_remove_file(cd, cd->devt_attr);
+
class_device_remove_attrs(class_dev);
kobject_hotplug(&class_dev->kobj, KOBJ_REMOVE);
_
--
Maneesh Soni
Linux Technology Center,
IBM India Software Labs,
Bangalore, India
email: [email protected]
Phone: 91-80-25044990
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