On Thu, Mar 09, 2006 at 08:28:24AM +0530, Maneesh Soni wrote:
> On Tue, Mar 07, 2006 at 11:53:42PM -0800, Greg KH wrote:
> > Hi,
> >
> > I spent some time tonight trying to track down how to fix the issue of
> > duplicate sysfs files and/or directories. This happens when you try to
> > create a kobject with the same name in the same directory. The creation
> > of the second kobject will fail, but the directory will remain in sysfs.
> >
>
> Let me understand this. Lets say we have sysfs directory tree like
> /sys/a/b/c
> and someone is trying to create one more kobject with name "c" for the
> parent kobject "b" ?
Yes.
> And are you saying that though the new creation fails but the existing
> directory remains in sysfs?
No. The new creation fails, but we end up with two "c" directories
under "b".
> I think failing the new creation and leaving the exisiting directoy is
> ok.
I agree, but that's not what happens :)
> But there is sysfs_dirent leakage which does need fixing.
Yes.
> > Now I know this isn't a normal operation, but it would be good to fix
> > this eventually. I traced the issue down to fs/sysfs/dir.c:create_dir()
> > and the check for:
> > if (error && (error != -EEXIST)) {
> >
> > Problem is, error is set to -EEXIST, so we don't clean up properly. Now
> > I know we can't just not check for this, as if you do that error
> > cleanup, the original kobject's sysfs entry gets very messed up (ls -l
> > does not like it at all...)
> >
> > But I can't seem to figure out what exactly we need to do to clean up
> > properly here.
> >
> > Do you, or anyone else, have any pointers or ideas?
> >
>
> If you are talking about the example above, to me it appears that except
> a possible sysfs_dirent leakage, we are some what ok, else there would have
> been more catastrophic results because of the duplicate directory dentry/inode.
>
> As per the current code
>
> static int create_dir(struct kobject * k, struct dentry * p,
> const char * n, struct dentry ** d)
> {
> int error;
> umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
>
> mutex_lock(&p->d_inode->i_mutex);
>
> *d = lookup_one_len(n, p, strlen(n));
>
> ^^^^ lookup_one_len() will return the existing dentry corresponding to
> the last component "c" in "/sys/a/b/c" without any error. Just note
> that VFS is not going to allocate a new dentry for it. The existing
> dentry's ref count will be increased by one.
>
> if (!IS_ERR(*d)) {
> error = sysfs_make_dirent(p->d_fsdata, *d, k, mode, SYSFS_DIR);
>
> ^^^^ we do have problem here, a new sysfs_dirent is allocated which
> replaces the existing dentry->d_fsdata and yuk... the old sysfs_dirent
> is no more linked with the existing directory, there by leaking
> one sysfs_dirent.
Yeah, I just couldn't figure out how to clean it up properly :)
> Not only for sysfs_create_dir(), I think the problem of existing sysfs_dirent
> is also there with sysfs_add_file() and sysfs_add_link(). I am working on a
> patch to plug this leak.
That's great, thanks.
I have a test module that shows this at:
http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/gregkh/sysfs-test.patch
just load the 'gregkh' module and look in /sys/class/gregkh/ to see the
duplicate "gregkh1" directories.
thanks,
greg k-h
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