Commit 26ea12de authored Sep 18, 2013 by Tejun Heo Committed by Greg Kroah-Hartman Oct 03, 2013

kobject: grab an extra reference on kobject->sd to allow duplicate deletes



sysfs currently has a rather weird behavior regarding removals.  A
directory removal would delete all files directly under it but
wouldn't recurse into subdirectories, which, while a bit inconsistent,
seems to make sense at the first glance as each directory is
supposedly associated with a kobject and each kobject can take care of
the directory deletion; however, this doesn't really hold as we have
groups which can be directories without a kobject associated with it
and require explicit deletions.

We're in the process of separating out sysfs from kboject / driver
core and want a consistent behavior.  A removal should delete either
only the specified node or everything under it.  I think it is helpful
to support recursive atomic removal and later patches will implement
it.

Such change means that a sysfs_dirent associated with kobject may be
deleted before the kobject itself is removed if one of its ancestor
gets removed before it.  As sysfs_remove_dir() puts the base ref, we
may end up with dangling pointer on descendants.  This can be solved
by holding an extra reference on the sd from kobject.

Acquire an extra reference on the associated sysfs_dirent on directory
creation and put it after removal.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent d69ac5a0

fs/sysfs/dir.c

+6 −1

Original line number	Original line	Diff line number	Diff line
	@@ -549,7 +549,12 @@ void sysfs_remove_one(struct sysfs_addrm_cxt acxt, struct sysfs_dirent sd)
	{		{
	struct sysfs_inode_attrs *ps_iattr;		struct sysfs_inode_attrs *ps_iattr;

	BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);		/*
			* Removal can be called multiple times on the same node. Only the
			* first invocation is effective and puts the base ref.
			*/
			if (sd->s_flags & SYSFS_FLAG_REMOVED)
			return;

	sysfs_unlink_sibling(sd);		sysfs_unlink_sibling(sd);

lib/kobject.c

+12 −0

Original line number	Original line	Diff line number	Diff line
	@@ -76,6 +76,13 @@ static int create_dir(struct kobject *kobj)
	if (error)		if (error)
	sysfs_remove_dir(kobj);		sysfs_remove_dir(kobj);
	}		}

			/*
			* @kobj->sd may be deleted by an ancestor going away. Hold an
			* extra reference so that it stays until @kobj is gone.
			*/
			sysfs_get(kobj->sd);

	return error;		return error;
	}		}

	@@ -532,10 +539,15 @@ out:
	*/		*/
	void kobject_del(struct kobject *kobj)		void kobject_del(struct kobject *kobj)
	{		{
			struct sysfs_dirent *sd;

	if (!kobj)		if (!kobj)
	return;		return;

			sd = kobj->sd;
	sysfs_remove_dir(kobj);		sysfs_remove_dir(kobj);
			sysfs_put(sd);

	kobj->state_in_sysfs = 0;		kobj->state_in_sysfs = 0;
	kobj_kset_leave(kobj);		kobj_kset_leave(kobj);
	kobject_put(kobj->parent);		kobject_put(kobj->parent);

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