Messages in this thread | | | Date | Wed, 8 Mar 2006 21:58:16 -0800 | From | Greg KH <> | Subject | Re: problem with duplicate sysfs directories and files |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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