From: Andrey Borzenkov <arvidjaar@mail.ru>
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:
- 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.
- 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.
fs/sysfs/dir.c | 12 ++++++++++--
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 2003-09-14 13:18:15.000000000 -0700
+++ 25-akpm/fs/sysfs/dir.c 2003-09-14 13:18:15.000000000 -0700
@@ -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 2003-09-14 13:18:15.000000000 -0700
+++ 25-akpm/lib/kobject.c 2003-09-14 13:18:15.000000000 -0700
@@ -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);
}
@@ -448,6 +446,8 @@ 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)
_