JFS: fine-grained xattr locking

Since the getxattr and listxattr iops no longer hold the i_sem, we can move
the xattr locking into another semaphore.  This allows us to simplify much
of the xattr and acl code that went to lengths to avoid recursively setting
i_sem.

fs/jfs/acl.c

@@ -123,11 +123,11 @@ int jfs_set_acl(struct inode *inode, int type, struct posix_acl *acl)
 }
 
 /*
- *	__jfs_permission()
+ *	jfs_permission()
  *
  * modified vfs_permission to check posix acl
  */
-static int __jfs_permission(struct inode * inode, int mask, int have_sem)
+int jfs_permission(struct inode * inode, int mask, struct nameidata *nd)
 {
 	umode_t mode = inode->i_mode;
 	struct jfs_inode_info *ji = JFS_IP(inode);
@@ -161,11 +161,7 @@ static int __jfs_permission(struct inode * inode, int mask, int have_sem)
 	if (ji->i_acl == JFS_ACL_NOT_CACHED) {
 		struct posix_acl *acl;
 
-		if (!have_sem)
-			down(&inode->i_sem);
 		acl = jfs_get_acl(inode, ACL_TYPE_ACCESS);
-		if (!have_sem)
-			up(&inode->i_sem);
 
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
@@ -208,14 +204,6 @@ static int __jfs_permission(struct inode * inode, int mask, int have_sem)
 
 	return -EACCES;
 }
-int jfs_permission(struct inode * inode, int mask, struct nameidata *nd)
-{
-	return __jfs_permission(inode, mask, 0);
-}
-int jfs_permission_have_sem(struct inode * inode, int mask)
-{
-	return __jfs_permission(inode, mask, 1);
-}
 
 int jfs_init_acl(struct inode *inode, struct inode *dir)
 {

fs/jfs/jfs_acl.h

@@ -24,7 +24,6 @@
 
 struct posix_acl *jfs_get_acl(struct inode *, int);
 int jfs_set_acl(struct inode *, int, struct posix_acl *);
-int jfs_permission_have_sem(struct inode *, int);
 int jfs_permission(struct inode *, int, struct nameidata *);
 int jfs_init_acl(struct inode *, struct inode *);
 int jfs_setattr(struct dentry *, struct iattr *);

fs/jfs/jfs_incore.h

@@ -67,6 +67,8 @@ struct jfs_inode_info {
 	 * inode is blocked in txBegin or TxBeginAnon
 	 */
 	struct semaphore commit_sem;
+	/* xattr_sem allows us to access the xattrs without taking i_sem */
+	struct rw_semaphore xattr_sem;
 	lid_t	xtlid;		/* lid of xtree lock on directory */
 #ifdef CONFIG_JFS_POSIX_ACL
 	struct posix_acl *i_acl;

fs/jfs/super.c

@@ -457,6 +457,7 @@ static void init_once(void *foo, kmem_cache_t * cachep, unsigned long flags)
 		INIT_LIST_HEAD(&jfs_ip->anon_inode_list);
 		init_rwsem(&jfs_ip->rdwrlock);
 		init_MUTEX(&jfs_ip->commit_sem);
+		init_rwsem(&jfs_ip->xattr_sem);
 		jfs_ip->atlhead = 0;
 		jfs_ip->active_ag = -1;
 #ifdef CONFIG_JFS_POSIX_ACL

fs/jfs/xattr.c

@@ -729,7 +729,7 @@ static int can_set_xattr(struct inode *inode, const char *name,
 		return -EPERM;
 
 #ifdef CONFIG_JFS_POSIX_ACL
-	return jfs_permission_have_sem(inode, MAY_WRITE);
+	return jfs_permission(inode, MAY_WRITE, NULL);
 #else
 	return permission(inode, MAY_WRITE, NULL);
 #endif
@@ -763,6 +763,8 @@ int __jfs_setxattr(struct inode *inode, const char *name, const void *value,
 		namelen -= XATTR_OS2_PREFIX_LEN;
 	}
 
+	down_write(&JFS_IP(inode)->xattr_sem);
+
 	xattr_size = ea_get(inode, &ea_buf, 0);
 	if (xattr_size < 0) {
 		rc = xattr_size;
@@ -868,6 +870,8 @@ int __jfs_setxattr(struct inode *inode, const char *name, const void *value,
       release:
 	ea_release(inode, &ea_buf);
       out:
+	up_write(&JFS_IP(inode)->xattr_sem);
+
 	if (os2name)
 		kfree(os2name);
 
@@ -890,8 +894,7 @@ static int can_get_xattr(struct inode *inode, const char *name)
 #ifdef CONFIG_JFS_POSIX_ACL
 	if(strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) == 0)
 		return 0;
-	else
-		return jfs_permission_have_sem(inode, MAY_READ);
+	return jfs_permission(inode, MAY_READ, NULL);
 #else
 	return permission(inode, MAY_READ, NULL);
 #endif
@@ -923,7 +926,10 @@ ssize_t __jfs_getxattr(struct inode *inode, const char *name, void *data,
 		namelen -= XATTR_OS2_PREFIX_LEN;
 	}
 
+	down_read(&JFS_IP(inode)->xattr_sem);
+
 	xattr_size = ea_get(inode, &ea_buf, 0);
+
 	if (xattr_size < 0) {
 		size = xattr_size;
 		goto out;
@@ -955,6 +961,8 @@ ssize_t __jfs_getxattr(struct inode *inode, const char *name, void *data,
       release:
 	ea_release(inode, &ea_buf);
       out:
+	up_read(&JFS_IP(inode)->xattr_sem);
+
 	if (os2name)
 		kfree(os2name);
 
@@ -966,15 +974,12 @@ ssize_t jfs_getxattr(struct dentry *dentry, const char *name, void *data,
 {
 	int err;
 
-	down(&dentry->d_inode->i_sem);
 	err = __jfs_getxattr(dentry->d_inode, name, data, buf_size);
-	up(&dentry->d_inode->i_sem);
 
 	return err;
 }
 
-static ssize_t __jfs_listxattr(struct dentry * dentry, char *data,
-			       size_t buf_size)
+ssize_t jfs_listxattr(struct dentry * dentry, char *data, size_t buf_size)
 {
 	struct inode *inode = dentry->d_inode;
 	char *buffer;
@@ -984,6 +989,8 @@ static ssize_t __jfs_listxattr(struct dentry * dentry, char *data,
 	struct jfs_ea *ea;
 	struct ea_buffer ea_buf;
 
+	down_read(&JFS_IP(inode)->xattr_sem);
+
 	xattr_size = ea_get(inode, &ea_buf, 0);
 	if (xattr_size < 0) {
 		size = xattr_size;
@@ -1017,20 +1024,10 @@ static ssize_t __jfs_listxattr(struct dentry * dentry, char *data,
       release:
 	ea_release(inode, &ea_buf);
       out:
+	up_read(&JFS_IP(inode)->xattr_sem);
 	return size;
 }
 
-ssize_t jfs_listxattr(struct dentry * dentry, char *data, size_t buf_size)
-{
-	int err;
-
-	down(&dentry->d_inode->i_sem);
-	err = __jfs_listxattr(dentry, data, buf_size);
-	up(&dentry->d_inode->i_sem);
-
-	return err;
-}
-
 int jfs_removexattr(struct dentry *dentry, const char *name)
 {
 	return __jfs_setxattr(dentry->d_inode, name, 0, 0, XATTR_REPLACE);