Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753615AbbFAPyD (ORCPT ); Mon, 1 Jun 2015 11:54:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45665 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751479AbbFAPxy (ORCPT ); Mon, 1 Jun 2015 11:53:54 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <21902.1433166736@warthog.procyon.org.uk> <16823.1433173503@warthog.procyon.org.uk> To: Miklos Szeredi Cc: dhowells@redhat.com, Al Viro , Kernel Mailing List , Linux-Fsdevel , "linux-unionfs@vger.kernel.org" Subject: Re: Can ovl_drop_write() be called earlier in ovl_dentry_open() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <17014.1433174029.1@warthog.procyon.org.uk> Date: Mon, 01 Jun 2015 16:53:49 +0100 Message-ID: <17015.1433174029@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1197 Lines: 31 Miklos Szeredi wrote: > >> Hmm, that could result in a race where remount r/o of upper fs comes > >> in between copy-up and vfs_open() so copy-up succeeds but the actual > >> open fails. It's harmless, though, and not very likely. So I guess > >> your patch is OK. > > > > That race is there anyway if there's no copy up, right? > > No. The race I'm talking about is that with your patch it's possible > that the file will be copied up, but open will return -EROFS. Ah, I see what you're getting at. > Without your patch, that is not possible since holding write counter > for the mnt over both the copy-up and the open ensures that the > filesystem cannot become read-only in the middle. > > So your patch changes behavior, but the new behavior is acceptable, > because there's no major change in semantics (it should only be > detectable by the increased disk usage in the rare case of the failed > open). Okay. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/