From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EE6CC31E45 for ; Thu, 13 Jun 2019 15:02:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D293521743 for ; Thu, 13 Jun 2019 15:02:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733108AbfFMPB4 (ORCPT ); Thu, 13 Jun 2019 11:01:56 -0400 Received: from fieldses.org ([173.255.197.46]:52414 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732521AbfFMObv (ORCPT ); Thu, 13 Jun 2019 10:31:51 -0400 Received: by fieldses.org (Postfix, from userid 2815) id 34E742012; Thu, 13 Jun 2019 10:31:51 -0400 (EDT) Date: Thu, 13 Jun 2019 10:31:51 -0400 From: "J . Bruce Fields" To: Miklos Szeredi Cc: Amir Goldstein , Jeff Layton , linux-fsdevel@vger.kernel.org, Linux NFS list , overlayfs Subject: Re: [PATCH v2] locks: eliminate false positive conflicts for write lease Message-ID: <20190613143151.GC2145@fieldses.org> References: <20190612172408.22671-1-amir73il@gmail.com> <20190612183156.GA27576@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jun 13, 2019 at 04:13:15PM +0200, Miklos Szeredi wrote: > On Wed, Jun 12, 2019 at 8:31 PM J . Bruce Fields wrote: > > > > How do opens for execute work? I guess they create a struct file with > > FMODE_EXEC and FMODE_RDONLY set and they decrement i_writecount. Do > > they also increment i_readcount? Reading do_open_execat and alloc_file, > > looks like it does, so, good, they should conflict with write leases, > > which sounds right. > > Right, but then why this: > > > > + /* Eliminate deny writes from actual writers count */ > > > + if (wcount < 0) > > > + wcount = 0; > > It's basically a no-op, as you say. And it doesn't make any sense > logically, since denying writes *should* deny write leases as well... Yes. I feel like the negative writecount case is a little nonobvious, so maybe replace that by a comment, something like this?: --b. diff --git a/fs/locks.c b/fs/locks.c index 2056595751e8..379829b913c1 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1772,11 +1772,12 @@ check_conflicting_open(struct file *filp, const long arg, int flags) if (arg == F_RDLCK && wcount > 0) return -EAGAIN; - /* Eliminate deny writes from actual writers count */ - if (wcount < 0) - wcount = 0; - - /* Make sure that only read/write count is from lease requestor */ + /* + * Make sure that only read/write count is from lease requestor. + * Note that this will result in denying write leases when wcount + * is negative, which is what we want. (We shouldn't grant + * write leases on files open for execution.) + */ if (filp->f_mode & FMODE_WRITE) self_wcount = 1; else if (filp->f_mode & FMODE_READ)