fuse: make fuse_permission() RCU aware

Only bail out of fuse_permission() on IPERM_FLAG_RCU when blocking is
actually necessary.

CC: Nick Piggin <npiggin@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/dir.c

@@ -970,6 +970,14 @@ static int fuse_access(struct inode *inode, int mask)
 	return err;
 }
 
+static int fuse_perm_getattr(struct inode *inode, int flags)
+{
+	if (flags & IPERM_FLAG_RCU)
+		return -ECHILD;
+
+	return fuse_do_getattr(inode, NULL, NULL);
+}
+
 /*
  * Check permission.  The two basic access models of FUSE are:
  *
@@ -989,9 +997,6 @@ static int fuse_permission(struct inode *inode, int mask, unsigned int flags)
 	bool refreshed = false;
 	int err = 0;
 
-	if (flags & IPERM_FLAG_RCU)
-		return -ECHILD;
-
 	if (!fuse_allow_task(fc, current))
 		return -EACCES;
 
@@ -1000,9 +1005,15 @@ static int fuse_permission(struct inode *inode, int mask, unsigned int flags)
 	 */
 	if ((fc->flags & FUSE_DEFAULT_PERMISSIONS) ||
 	    ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))) {
-		err = fuse_update_attributes(inode, NULL, NULL, &refreshed);
-		if (err)
-			return err;
+		struct fuse_inode *fi = get_fuse_inode(inode);
+
+		if (fi->i_time < get_jiffies_64()) {
+			refreshed = true;
+
+			err = fuse_perm_getattr(inode, flags);
+			if (err)
+				return err;
+		}
 	}
 
 	if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
@@ -1012,7 +1023,7 @@ static int fuse_permission(struct inode *inode, int mask, unsigned int flags)
 		   attributes.  This is also needed, because the root
 		   node will at first have no permissions */
 		if (err == -EACCES && !refreshed) {
-			err = fuse_do_getattr(inode, NULL, NULL);
+			err = fuse_perm_getattr(inode, flags);
 			if (!err)
 				err = generic_permission(inode, mask,
 							flags, NULL);
@@ -1023,13 +1034,16 @@ static int fuse_permission(struct inode *inode, int mask, unsigned int flags)
 		   noticed immediately, only after the attribute
 		   timeout has expired */
 	} else if (mask & (MAY_ACCESS | MAY_CHDIR)) {
+		if (flags & IPERM_FLAG_RCU)
+			return -ECHILD;
+
 		err = fuse_access(inode, mask);
 	} else if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode)) {
 		if (!(inode->i_mode & S_IXUGO)) {
 			if (refreshed)
 				return -EACCES;
 
-			err = fuse_do_getattr(inode, NULL, NULL);
+			err = fuse_perm_getattr(inode, flags);
 			if (!err && !(inode->i_mode & S_IXUGO))
 				return -EACCES;
 		}