sysfs: implement kobj_sysfs_assoc_lock

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 8 insertions, 1 deletions

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 07912269567..e9fddcc5944 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -15,6 +15,7 @@
 
 DECLARE_RWSEM(sysfs_rename_sem);
 spinlock_t sysfs_lock = SPIN_LOCK_UNLOCKED;
+spinlock_t kobj_sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;
 
 static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
 static DEFINE_IDA(sysfs_ino_ida);
@@ -426,8 +427,13 @@ 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 39ab0481379..718e2e123fa 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -62,6 +62,7 @@ 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 sysfs_lock;
+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;