sysfs: Gut sysfs_addrm_start and sysfs_addrm_finish

With lazy inode updates and dentry operations bringing everything
into sync on demand there is no longer any need to immediately
update the vfs or grab i_mutex to protect those updates as we
make changes to sysfs.

Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/dir.c

@@ -386,12 +386,6 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
 	return NULL;
 }
 
-static int sysfs_ilookup_test(struct inode *inode, void *arg)
-{
-	struct sysfs_dirent *sd = arg;
-	return inode->i_ino == sd->s_ino;
-}
-
 /**
  *	sysfs_addrm_start - prepare for sysfs_dirent add/remove
  *	@acxt: pointer to sysfs_addrm_cxt to be used
@@ -399,47 +393,20 @@ static int sysfs_ilookup_test(struct inode *inode, void *arg)
  *
  *	This function is called when the caller is about to add or
  *	remove sysfs_dirent under @parent_sd.  This function acquires
- *	sysfs_mutex, grabs inode for @parent_sd if available and lock
- *	i_mutex of it.  @acxt is used to keep and pass context to
+ *	sysfs_mutex.  @acxt is used to keep and pass context to
  *	other addrm functions.
  *
  *	LOCKING:
  *	Kernel thread context (may sleep).  sysfs_mutex is locked on
- *	return.  i_mutex of parent inode is locked on return if
- *	available.
+ *	return.
  */
 void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
 		       struct sysfs_dirent *parent_sd)
 {
-	struct inode *inode;
-
 	memset(acxt, 0, sizeof(*acxt));
 	acxt->parent_sd = parent_sd;
 
-	/* Lookup parent inode.  inode initialization is protected by
-	 * sysfs_mutex, so inode existence can be determined by
-	 * looking up inode while holding sysfs_mutex.
-	 */
 	mutex_lock(&sysfs_mutex);
-
-	inode = ilookup5(sysfs_sb, parent_sd->s_ino, sysfs_ilookup_test,
-			 parent_sd);
-	if (inode) {
-		WARN_ON(inode->i_state & I_NEW);
-
-		/* parent inode available */
-		acxt->parent_inode = inode;
-
-		/* sysfs_mutex is below i_mutex in lock hierarchy.
-		 * First, trylock i_mutex.  If fails, unlock
-		 * sysfs_mutex and lock them in order.
-		 */
-		if (!mutex_trylock(&inode->i_mutex)) {
-			mutex_unlock(&sysfs_mutex);
-			mutex_lock(&inode->i_mutex);
-			mutex_lock(&sysfs_mutex);
-		}
-	}
 }
 
 /**
@@ -471,11 +438,6 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 
 	sd->s_parent = sysfs_get(acxt->parent_sd);
 
-	if (sysfs_type(sd) == SYSFS_DIR && acxt->parent_inode)
-		inc_nlink(acxt->parent_inode);
-
-	acxt->cnt++;
-
 	sysfs_link_sibling(sd);
 
 	/* Update timestamps on the parent */
@@ -579,40 +541,6 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 	sd->s_flags |= SYSFS_FLAG_REMOVED;
 	sd->s_sibling = acxt->removed;
 	acxt->removed = sd;
-
-	if (sysfs_type(sd) == SYSFS_DIR && acxt->parent_inode)
-		drop_nlink(acxt->parent_inode);
-
-	acxt->cnt++;
-}
-
-/**
- *	sysfs_dec_nlink - Decrement link count for the specified sysfs_dirent
- *	@sd: target sysfs_dirent
- *
- *	Decrement nlink for @sd.  @sd must have been unlinked from its
- *	parent on entry to this function such that it can't be looked
- *	up anymore.
- */
-static void sysfs_dec_nlink(struct sysfs_dirent *sd)
-{
-	struct inode *inode;
-
-	inode = ilookup(sysfs_sb, sd->s_ino);
-	if (!inode)
-		return;
-
-	/* adjust nlink and update timestamp */
-	mutex_lock(&inode->i_mutex);
-
-	inode->i_ctime = CURRENT_TIME;
-	drop_nlink(inode);
-	if (sysfs_type(sd) == SYSFS_DIR)
-		drop_nlink(inode);
-
-	mutex_unlock(&inode->i_mutex);
-
-	iput(inode);
 }
 
 /**
@@ -621,25 +549,15 @@ static void sysfs_dec_nlink(struct sysfs_dirent *sd)
  *
  *	Finish up sysfs_dirent add/remove.  Resources acquired by
  *	sysfs_addrm_start() are released and removed sysfs_dirents are
- *	cleaned up.  Timestamps on the parent inode are updated.
+ *	cleaned up.
  *
  *	LOCKING:
- *	All mutexes acquired by sysfs_addrm_start() are released.
+ *	sysfs_mutex is released.
  */
 void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
 {
 	/* release resources acquired by sysfs_addrm_start() */
 	mutex_unlock(&sysfs_mutex);
-	if (acxt->parent_inode) {
-		struct inode *inode = acxt->parent_inode;
-
-		/* if added/removed, update timestamps on the parent */
-		if (acxt->cnt)
-			inode->i_ctime = inode->i_mtime = CURRENT_TIME;
-
-		mutex_unlock(&inode->i_mutex);
-		iput(inode);
-	}
 
 	/* kill removed sysfs_dirents */
 	while (acxt->removed) {
@@ -648,7 +566,6 @@ void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
 		acxt->removed = sd->s_sibling;
 		sd->s_sibling = NULL;
 
-		sysfs_dec_nlink(sd);
 		sysfs_deactivate(sd);
 		unmap_bin_file(sd);
 		sysfs_put(sd);

fs/sysfs/sysfs.h

@@ -89,9 +89,7 @@ static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
  */
 struct sysfs_addrm_cxt {
 	struct sysfs_dirent	*parent_sd;
-	struct inode		*parent_inode;
 	struct sysfs_dirent	*removed;
-	int			cnt;
 };
 
 /*