sysfs: restructure add/remove paths and fix inode update

The original add/remove code had the following problems.

* parent's timestamps are updated on dentry instantiation.  this is
  incorrect with reclaimable files.

* updating parent's timestamps isn't synchronized.

* parent nlink update assumes the inode is accessible which won't be
  true once directory dentries are made reclaimable.

This patch restructures add/remove paths to resolve the above
problems.  Add/removal are done in the following steps.

1. sysfs_addrm_start() : acquire locks including sysfs_mutex and other
   resources.

2-a. sysfs_add_one() : add new sd.  linking the new sd into the
     children list is caller's responsibility.

2-b. sysfs_remove_one() : remove a sd.  unlinking the sd from the
     children list is caller's responsibility.

3. sysfs_addrm_finish() : release all resources and clean up.

Steps 2-a and/or 2-b can be repeated multiple times.

Parent's inode is looked up during sysfs_addrm_start().  If available
(always at the moment), it's pinned and nlink is updated as sd's are
added and removed.  Timestamps are updated during finish if any sd has
been added or removed.  If parent's inode is not available during
start, sysfs_mutex ensures that parent inode is not created till
add/remove is complete.

All the complexity is contained inside the helper functions.
Especially, dentry/inode handling is properly hidden from the rest of
sysfs which now mostly operate on sysfs_dirents.  As an added bonus,
codes which use these helpers to add and remove sysfs_dirents are now
more structured and simpler.

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

1 files changed, 8 insertions, 38 deletions

diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index d439c0b4bfc..f95966847a8 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -191,15 +191,9 @@ void sysfs_instantiate(struct dentry *dentry, struct inode *inode)
 {
 	BUG_ON(!dentry || dentry->d_inode);
 
-	if (inode->i_state & I_NEW) {
+	if (inode->i_state & I_NEW)
 		unlock_new_inode(inode);
 
-		if (dentry->d_parent && dentry->d_parent->d_inode) {
-			struct inode *p_inode = dentry->d_parent->d_inode;
-			p_inode->i_mtime = p_inode->i_ctime = CURRENT_TIME;
-		}
-	}
-
 	d_instantiate(dentry, inode);
 }
 
@@ -220,7 +214,6 @@ void sysfs_instantiate(struct dentry *dentry, struct inode *inode)
 void sysfs_drop_dentry(struct sysfs_dirent *sd)
 {
 	struct dentry *dentry = NULL;
-	struct timespec curtime;
 	struct inode *inode;
 
 	/* We're not holding a reference to ->s_dentry dentry but the
@@ -246,13 +239,11 @@ void sysfs_drop_dentry(struct sysfs_dirent *sd)
 		dput(dentry);
 
 	/* adjust nlink and update timestamp */
-	curtime = CURRENT_TIME;
-
 	inode = ilookup(sysfs_sb, sd->s_ino);
 	if (inode) {
 		mutex_lock(&inode->i_mutex);
 
-		inode->i_ctime = curtime;
+		inode->i_ctime = CURRENT_TIME;
 		drop_nlink(inode);
 		if (sysfs_type(sd) == SYSFS_DIR)
 			drop_nlink(inode);
@@ -260,30 +251,17 @@ void sysfs_drop_dentry(struct sysfs_dirent *sd)
 		mutex_unlock(&inode->i_mutex);
 		iput(inode);
 	}
-
-	/* adjust nlink and udpate timestamp of the parent */
-	inode = ilookup(sysfs_sb, sd->s_parent->s_ino);
-	if (inode) {
-		mutex_lock(&inode->i_mutex);
-
-		inode->i_ctime = inode->i_mtime = curtime;
-		if (sysfs_type(sd) == SYSFS_DIR)
-			drop_nlink(inode);
-
-		mutex_unlock(&inode->i_mutex);
-		iput(inode);
-	}
 }
 
 int sysfs_hash_and_remove(struct sysfs_dirent *dir_sd, const char *name)
 {
+	struct sysfs_addrm_cxt acxt;
 	struct sysfs_dirent **pos, *sd;
-	int found = 0;
 
 	if (!dir_sd)
 		return -ENOENT;
 
-	mutex_lock(&sysfs_mutex);
+	sysfs_addrm_start(&acxt, dir_sd);
 
 	for (pos = &dir_sd->s_children; *pos; pos = &(*pos)->s_sibling) {
 		sd = *pos;
@@ -291,22 +269,14 @@ int sysfs_hash_and_remove(struct sysfs_dirent *dir_sd, const char *name)
 		if (!sysfs_type(sd))
 			continue;
 		if (!strcmp(sd->s_name, name)) {
-			sd->s_flags |= SYSFS_FLAG_REMOVED;
 			*pos = sd->s_sibling;
 			sd->s_sibling = NULL;
-			found = 1;
+			sysfs_remove_one(&acxt, sd);
 			break;
 		}
 	}
 
-	mutex_unlock(&sysfs_mutex);
-
-	if (!found)
-		return -ENOENT;
-
-	sysfs_drop_dentry(sd);
-	sysfs_deactivate(sd);
-	sysfs_put(sd);
-
-	return 0;
+	if (sysfs_addrm_finish(&acxt))
+		return 0;
+	return -ENOENT;
 }