sysfs: reimplement symlink using sysfs_dirent tree

sysfs symlink is implemented by referencing dentry and kobject from
sysfs_dirent - symlink entry references kobject, dentry is used to
walk the tree.  This complicates object lifetimes rules and is
dangerous - for example, there is no way to tell to which module the
target of a symlink belongs and referencing that kobject can make it
linger after the module is gone.

This patch reimplements symlink using only sysfs_dirent tree.  sd for
a symlink points and holds reference to the target sysfs_dirent and
all walking is done using sysfs_dirent tree.  Simpler and safer.

Please read the following message for more info.

  http://article.gmane.org/gmane.linux.kernel/510293

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index e9fddcc59447..2a94dc36d166 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -54,7 +54,7 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
         parent_sd = sd->s_parent;
 
         if (sd->s_type & SYSFS_KOBJ_LINK)
-                kobject_put(sd->s_elem.symlink.target_kobj);
+                sysfs_put(sd->s_elem.symlink.target_sd);
         if (sd->s_type & SYSFS_COPY_NAME)
                 kfree(sd->s_name);
         kfree(sd->s_iattr);