ovl: concurrent copy up of regular files

Now that copy up of regular file is done using O_TMPFILE,
we don't need to hold rename_lock throughout copy up.

Use the copy up waitqueue to synchronize concurrent copy up
of the same file. Different regular files can be copied up
concurrently.

The upper dir inode_lock is taken instead of rename_lock,
because it is needed for lookup and later for linking the
temp file, but it is released while copying up data.
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -291,7 +291,16 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
 		BUG_ON(upperpath.dentry != NULL);
 		upperpath.dentry = temp;
 
-		err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
+		if (tmpfile) {
+			inode_unlock(udir);
+			err = ovl_copy_up_data(lowerpath, &upperpath,
+					       stat->size);
+			inode_lock_nested(udir, I_MUTEX_PARENT);
+		} else {
+			err = ovl_copy_up_data(lowerpath, &upperpath,
+					       stat->size);
+		}
+
 		if (err)
 			goto out_cleanup;
 	}
@@ -353,8 +362,6 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	struct dentry *upperdir;
 	const char *link = NULL;
 	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
-	/* Should we copyup with O_TMPFILE or with workdir? */
-	bool tmpfile = S_ISREG(stat->mode) && ofs->tmpfile;
 
 	if (WARN_ON(!workdir))
 		return -EROFS;
@@ -374,6 +381,25 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 			return PTR_ERR(link);
 	}
 
+	/* Should we copyup with O_TMPFILE or with workdir? */
+	if (S_ISREG(stat->mode) && ofs->tmpfile) {
+		err = ovl_copy_up_start(dentry);
+		/* err < 0: interrupted, err > 0: raced with another copy-up */
+		if (unlikely(err)) {
+			pr_debug("ovl_copy_up_start(%pd2) = %i\n", dentry, err);
+			if (err > 0)
+				err = 0;
+			goto out_done;
+		}
+
+		inode_lock_nested(upperdir->d_inode, I_MUTEX_PARENT);
+		err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
+					 stat, link, &pstat, true);
+		inode_unlock(upperdir->d_inode);
+		ovl_copy_up_end(dentry);
+		goto out_done;
+	}
+
 	err = -EIO;
 	if (lock_rename(workdir, upperdir) != NULL) {
 		pr_err("overlayfs: failed to lock workdir+upperdir\n");
@@ -386,9 +412,10 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	}
 
 	err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
-				 stat, link, &pstat, tmpfile);
+				 stat, link, &pstat, false);
 out_unlock:
 	unlock_rename(workdir, upperdir);
+out_done:
 	do_delayed_call(&done);
 
 	return err;