fs: scale inode alias list

Add a new lock, dcache_inode_lock, to protect the inode's i_dentry list
from concurrent modification. d_alias is also protected by d_lock.
Signed-off-by: Nick Piggin <npiggin@kernel.dk>

fs/9p/vfs_inode.c

@@ -271,9 +271,11 @@ static struct dentry *v9fs_dentry_from_dir_inode(struct inode *inode)
 	struct dentry *dentry;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&dcache_inode_lock);
 	/* Directory should have only one entry. */
 	BUG_ON(S_ISDIR(inode->i_mode) && !list_is_singular(&inode->i_dentry));
 	dentry = list_entry(inode->i_dentry.next, struct dentry, d_alias);
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 	return dentry;
 }

fs/affs/amigaffs.c

@@ -129,6 +129,7 @@ affs_fix_dcache(struct dentry *dentry, u32 entry_ino)
 	struct list_head *head, *next;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&dcache_inode_lock);
 	head = &inode->i_dentry;
 	next = head->next;
 	while (next != head) {
@@ -139,6 +140,7 @@ affs_fix_dcache(struct dentry *dentry, u32 entry_ino)
 		}
 		next = next->next;
 	}
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 }
 

fs/cifs/inode.c

@@ -810,12 +810,15 @@ inode_has_hashed_dentries(struct inode *inode)
 	struct dentry *dentry;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&dcache_inode_lock);
 	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
 		if (!d_unhashed(dentry) || IS_ROOT(dentry)) {
+			spin_unlock(&dcache_inode_lock);
 			spin_unlock(&dcache_lock);
 			return true;
 		}
 	}
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 	return false;
 }

fs/exportfs/expfs.c

@@ -48,8 +48,10 @@ find_acceptable_alias(struct dentry *result,
 		return result;
 
 	spin_lock(&dcache_lock);
+	spin_lock(&dcache_inode_lock);
 	list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
 		dget_locked(dentry);
+		spin_unlock(&dcache_inode_lock);
 		spin_unlock(&dcache_lock);
 		if (toput)
 			dput(toput);
@@ -58,8 +60,10 @@ find_acceptable_alias(struct dentry *result,
 			return dentry;
 		}
 		spin_lock(&dcache_lock);
+		spin_lock(&dcache_inode_lock);
 		toput = dentry;
 	}
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 
 	if (toput)

fs/nfs/getroot.c

@@ -64,7 +64,11 @@ static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *i
 		 * Oops, since the test for IS_ROOT() will fail.
 		 */
 		spin_lock(&dcache_lock);
+		spin_lock(&dcache_inode_lock);
+		spin_lock(&sb->s_root->d_lock);
 		list_del_init(&sb->s_root->d_alias);
+		spin_unlock(&sb->s_root->d_lock);
+		spin_unlock(&dcache_inode_lock);
 		spin_unlock(&dcache_lock);
 	}
 	return 0;

fs/notify/fsnotify.c

@@ -60,6 +60,7 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 	watched = fsnotify_inode_watches_children(inode);
 
 	spin_lock(&dcache_lock);
+	spin_lock(&dcache_inode_lock);
 	/* run all of the dentries associated with this inode.  Since this is a
 	 * directory, there damn well better only be one item on this list */
 	list_for_each_entry(alias, &inode->i_dentry, d_alias) {
@@ -82,6 +83,7 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 		}
 		spin_unlock(&alias->d_lock);
 	}
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 }
 

fs/ocfs2/dcache.c

@@ -170,7 +170,7 @@ struct dentry *ocfs2_find_local_alias(struct inode *inode,
 	struct dentry *dentry = NULL;
 
 	spin_lock(&dcache_lock);
-
+	spin_lock(&dcache_inode_lock);
 	list_for_each(p, &inode->i_dentry) {
 		dentry = list_entry(p, struct dentry, d_alias);
 
@@ -188,6 +188,7 @@ struct dentry *ocfs2_find_local_alias(struct inode *inode,
 		dentry = NULL;
 	}
 
+	spin_unlock(&dcache_inode_lock);
 	spin_unlock(&dcache_lock);
 
 	return dentry;

include/linux/dcache.h

@@ -181,6 +181,7 @@ struct dentry_operations {
 
 #define DCACHE_CANT_MOUNT	0x0100
 
+extern spinlock_t dcache_inode_lock;
 extern spinlock_t dcache_lock;
 extern seqlock_t rename_lock;