Messages in this thread Patch in this message | | | Date | Mon, 8 Dec 2003 14:48:10 -0800 | From | Greg KH <> | Subject | oopses in kobjects in 2.6.0-test11 (was Re: kobject patch) |
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Ok, I'm ccing lkml and everyone else who has been in on this thread at different times. This is based on a patch from Andrey that was/is in the -mm tree for a while.
On Mon, Dec 08, 2003 at 02:25:26PM -0800, Greg KH wrote: > On Thu, Oct 09, 2003 at 01:48:37AM -0700, Andrew Morton wrote: > > > > I've had this in -mm for a while. What to do with it? > > Heh, nothing like digging up something from the past that I insisted was > not needed, but... > > > It is possible that parent is removed before child when child is in use. > > Trivial example is mounted USB storage when you unplug it. The kobject for > > USB device is removed but subordinate SCSI device remains. Then kernel oopses > > on attempt to release child e.g. umount removed USB storage. This patch fixes > > two problems: > > Yes, I now think this patch needs to be applied. I can easily cause a > parent device in sysfs to go away, with the child still present: > - plug in a usb-serial device > - run 'cat /dev/ttyUSB0' > - yank the device out. > Now if you cancel the 'cat' program, lovely oopses... > > So, Andrew, very sorry about this, but this patch should be sent to > Linus. I think Pat agrees with me, but he's on the road for a few days. > You might want to wait for him.
Hm, wait, Pat objected to the patch to kobject.c (now that I went back and read the whole thread.) And I agree with him, but I'm now getting an oops in get_kobj_path_length if I do the above while loading down the machine with other tasks when I cancel 'cat'.
So something else bad is happening here...
> > - kset_hotplug. It oopses in get_kobj_path_length because child->parent > > points to nowhere - even if parent has not yet been overwritten, its name > > is already freed. > > > > The patch moves kobject_put for parent from unlink() into > > kobject_cleanup for child making sure reference to parents exists for as > > long as child is there and may use it.
But you can't do this, as you need that kobject_put() in unlink() for when it is called from kobject_add().
Hm, wait... I think we are close...
Ok, here's how a parent can be removed from the system without the child going away: - create parent and register it successfully. - create child, call kobject_add() which increments the count of the parent. - call kobject_get() on the child. - call kobject_del() on the parent. This will keep the parent around, as the child still has a reference on it. - call kobject_del() on the child. This will decrement the count on the parent due to the call in unlink(). That will free the parent up from memory. But this child still has a incremented count (rightly, as it is in use). - So the child now has a stale parent pointer, causing all sorts of fun...
I'll work on a patch for kobject.c and post it in the next message, and include the original message and patch below for others to see.
thanks,
greg k-h
> > - after this oops has been fixed I got next one now in sysfs. The > > problem is sysfs_remove_dir would unlink all children including > > directories for subordinate kobjects. Resulting in dget/dput mismatch. > > I usually got oops due to the fact that d_delete in remove_dir would free > > inode and then simple_rmdir would try to access it. > > > > The patch avoids calling extra d_delete/unlink on already-deleted > > dentry. I hate this patch but anything better apparently requires > > complete redesign of sysfs implementation. Unlinking busy directory is > > otherwise impossible and I am afraid it will show itself somewhere else. > > > > > > > > 25-akpm/fs/sysfs/dir.c | 12 ++++++++++-- > > 25-akpm/lib/kobject.c | 4 ++-- > > 2 files changed, 12 insertions(+), 4 deletions(-) > > > > diff -puN fs/sysfs/dir.c~kobject-oops-fixes fs/sysfs/dir.c > > --- 25/fs/sysfs/dir.c~kobject-oops-fixes Thu Oct 9 01:46:51 2003 > > +++ 25-akpm/fs/sysfs/dir.c Thu Oct 9 01:46:51 2003 > > @@ -82,8 +82,16 @@ static void remove_dir(struct dentry * d > > { > > struct dentry * parent = dget(d->d_parent); > > down(&parent->d_inode->i_sem); > > - d_delete(d); > > - simple_rmdir(parent->d_inode,d); > > + /* > > + * It is possible that parent has already been removed, in which > > + * case directory is already unhashed and dput. > > + * Note that this won't update parent->d_inode->i_nlink; OTOH > > + * parent should already be dead > > + */ > > + if (!d_unhashed(d)) { > > + d_delete(d); > > + simple_rmdir(parent->d_inode,d); > > + } > > > > pr_debug(" o %s removing done (%d)\n",d->d_name.name, > > atomic_read(&d->d_count)); > > diff -puN lib/kobject.c~kobject-oops-fixes lib/kobject.c > > --- 25/lib/kobject.c~kobject-oops-fixes Thu Oct 9 01:46:51 2003 > > +++ 25-akpm/lib/kobject.c Thu Oct 9 01:46:51 2003 > > @@ -236,8 +236,6 @@ static void unlink(struct kobject * kobj > > list_del_init(&kobj->entry); > > up_write(&kobj->kset->subsys->rwsem); > > } > > - if (kobj->parent) > > - kobject_put(kobj->parent); > > kobject_put(kobj); > > } > > > > @@ -457,6 +455,8 @@ void kobject_cleanup(struct kobject * ko > > if (kobj->k_name != kobj->name) > > kfree(kobj->k_name); > > kobj->k_name = NULL; > > + if (kobj->parent) > > + kobject_put(kobj->parent); > > if (t && t->release) > > t->release(kobj); > > if (s) > > > > _ - 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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