fuse: truncate on spontaneous size change

Memory mappings were only truncated on an explicit truncate, but not when the
file size was changed externally.

Fix this by moving the truncation code from fuse_setattr to
fuse_change_attributes.

Yes, there are races between write and and external truncation, but we can't
really do anything about them.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fuse/dir.c

@@ -980,23 +980,6 @@ static void iattr_to_fattr(struct iattr *iattr, struct fuse_setattr_in *arg)
 	}
 }
 
-static void fuse_vmtruncate(struct inode *inode, loff_t offset)
-{
-	struct fuse_conn *fc = get_fuse_conn(inode);
-	int need_trunc;
-
-	spin_lock(&fc->lock);
-	need_trunc = inode->i_size > offset;
-	i_size_write(inode, offset);
-	spin_unlock(&fc->lock);
-
-	if (need_trunc) {
-		struct address_space *mapping = inode->i_mapping;
-		unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
-		truncate_inode_pages(mapping, offset);
-	}
-}
-
 /*
  * Set attributes, and at the same time refresh them.
  *
@@ -1014,7 +997,6 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr)
 	struct fuse_setattr_in inarg;
 	struct fuse_attr_out outarg;
 	int err;
-	int is_truncate = 0;
 
 	if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
 		err = inode_change_ok(inode, attr);
@@ -1024,7 +1006,6 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr)
 
 	if (attr->ia_valid & ATTR_SIZE) {
 		unsigned long limit;
-		is_truncate = 1;
 		if (IS_SWAPFILE(inode))
 			return -ETXTBSY;
 		limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
@@ -1051,21 +1032,20 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr)
 	request_send(fc, req);
 	err = req->out.h.error;
 	fuse_put_request(fc, req);
-	if (!err) {
+	if (err) {
+		if (err == -EINTR)
+			fuse_invalidate_attr(inode);
+		return err;
+	}
+
 	if ((inode->i_mode ^ outarg.attr.mode) & S_IFMT) {
 		make_bad_inode(inode);
-			err = -EIO;
-		} else {
-			if (is_truncate)
-				fuse_vmtruncate(inode, outarg.attr.size);
-			fuse_change_attributes(inode, &outarg.attr);
-			fi->i_time = time_to_jiffies(outarg.attr_valid,
-						     outarg.attr_valid_nsec);
+		return -EIO;
 	}
-	} else if (err == -EINTR)
-		fuse_invalidate_attr(inode);
 
-	return err;
+	fuse_change_attributes(inode, &outarg.attr);
+	fi->i_time = time_to_jiffies(outarg.attr_valid, outarg.attr_valid_nsec);
+	return 0;
 }
 
 static int fuse_getattr(struct vfsmount *mnt, struct dentry *entry,

fs/fuse/inode.c

@@ -109,20 +109,24 @@ static int fuse_remount_fs(struct super_block *sb, int *flags, char *data)
 	return 0;
 }
 
+static void fuse_truncate(struct address_space *mapping, loff_t offset)
+{
+	/* See vmtruncate() */
+	unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
+	truncate_inode_pages(mapping, offset);
+	unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
+}
+
 void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	if (S_ISREG(inode->i_mode) && i_size_read(inode) != attr->size)
-		invalidate_mapping_pages(inode->i_mapping, 0, -1);
+	loff_t oldsize;
 
 	inode->i_ino     = attr->ino;
 	inode->i_mode    = (inode->i_mode & S_IFMT) + (attr->mode & 07777);
 	inode->i_nlink   = attr->nlink;
 	inode->i_uid     = attr->uid;
 	inode->i_gid     = attr->gid;
-	spin_lock(&fc->lock);
-	i_size_write(inode, attr->size);
-	spin_unlock(&fc->lock);
 	inode->i_blocks  = attr->blocks;
 	inode->i_atime.tv_sec   = attr->atime;
 	inode->i_atime.tv_nsec  = attr->atimensec;
@@ -130,6 +134,17 @@ void fuse_change_attributes(struct inode *inode, struct fuse_attr *attr)
 	inode->i_mtime.tv_nsec  = attr->mtimensec;
 	inode->i_ctime.tv_sec   = attr->ctime;
 	inode->i_ctime.tv_nsec  = attr->ctimensec;
+
+	spin_lock(&fc->lock);
+	oldsize = inode->i_size;
+	i_size_write(inode, attr->size);
+	spin_unlock(&fc->lock);
+
+	if (S_ISREG(inode->i_mode) && oldsize != attr->size) {
+		if (attr->size < oldsize)
+			fuse_truncate(inode->i_mapping, attr->size);
+		invalidate_mapping_pages(inode->i_mapping, 0, -1);
+	}
 }
 
 static void fuse_init_inode(struct inode *inode, struct fuse_attr *attr)