[PATCH 09/14] sysfs: implement kobj_sysfs_assoc_lock

[Tejun Heo <htejun@gmail.com>]

kobj->dentry can go away anytime unless the user controls when the
associated sysfs node is deleted.  This patch implements
kobj_sysfs_assoc_lock which protects kobj->dentry.  This will be used
to maintain kobj based API when converting sysfs to use sysfs_dirent
tree instead of dentry/kobject.

Note that this lock belongs to kobject/driver-model not sysfs.  Once
sysfs is converted to not use kobject in its interface, this can be
removed from sysfs.

This is in preparation of object reference simplification.

Signed-off-by: Tejun Heo <htejun@gmail.com>
---
 fs/sysfs/dir.c   |    8 +++++++-
 fs/sysfs/sysfs.h |    1 +
 2 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 4070dc4..707eba9 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -13,6 +13,7 @@
 #include "sysfs.h"
 
 DECLARE_RWSEM(sysfs_rename_sem);
+spinlock_t kobj_sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;
 
 void release_sysfs_dirent(struct sysfs_dirent * sd)
 {
@@ -371,8 +372,13 @@ static void __sysfs_remove_dir(struct dentry *dentry)
 
 void sysfs_remove_dir(struct kobject * kobj)
 {
-	__sysfs_remove_dir(kobj->dentry);
+	struct dentry *d = kobj->dentry;
+
+	spin_lock(&kobj_sysfs_assoc_lock);
 	kobj->dentry = NULL;
+	spin_unlock(&kobj_sysfs_assoc_lock);
+
+	__sysfs_remove_dir(d);
 }
 
 int sysfs_rename_dir(struct kobject * kobj, struct dentry *new_parent,
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index b1a8a7e..5c41fc5 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -60,6 +60,7 @@ extern void sysfs_remove_subdir(struct dentry *);
 extern void sysfs_drop_dentry(struct sysfs_dirent *sd, struct dentry *parent);
 extern int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
 
+extern spinlock_t kobj_sysfs_assoc_lock;
 extern struct rw_semaphore sysfs_rename_sem;
 extern struct super_block * sysfs_sb;
 extern const struct file_operations sysfs_dir_operations;
-- 
1.5.0.3