[PATCH] fix kernel BUG at fs/sysfs/dir.c:20!

On Thu, Nov 04, 2004 at 12:52:38PM -0800, Greg KH wrote:
> Hi,
>
> I get the following BUG in the sysfs code when I do:
> 	- plug in a usb-serial device.
> 	- open the port with 'cat /dev/ttyUSB0'
> 	- unplug the device.
> 	- stop the 'cat' process with control-C
>
> This used to work just fine before your big sysfs changes.

There is a similar problem reported by s390 people where we see parent
kobject (directory) going away before child kobject (sub-directory). It
seems kobject code is able to handle this, but not the sysfs. What could
be happening that in sysfs_remove_dir() of parent directory, we try to
remove its contents. It works well with the regular files as it is the
final removal for sysfs_dirent corresponding to the files. But in case
of sub-directory we are doing an extra sysfs_put().  Once while removing
parent and the other one being the one from when sysfs_remove_dir() is
called for the child.

The following patch worked for the s390 people, I hope same will work in
this case also.


o Do not remove sysfs_dirents corresponding to the sub-directory in
  sysfs_remove_dir(). They will be removed in the sysfs_remove_dir() call
  for the specific sub-directory.
Signed-off-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

fs/sysfs/dir.c

@@ -277,7 +277,7 @@ void sysfs_remove_dir(struct kobject * kobj)
 	pr_debug("sysfs %s: removing dir\n",dentry->d_name.name);
 	down(&dentry->d_inode->i_sem);
 	list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {
-		if (!sd->s_element)
+		if (!sd->s_element || !(sd->s_type & SYSFS_NOT_PINNED))
 			continue;
 		list_del_init(&sd->s_sibling);
 		sysfs_drop_dentry(sd, dentry);