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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 3C82CC3A5A2 for ; Mon, 19 Aug 2019 21:53:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B7C9214DA for ; Mon, 19 Aug 2019 21:53:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728563AbfHSVx1 (ORCPT ); Mon, 19 Aug 2019 17:53:27 -0400 Received: from mga18.intel.com ([134.134.136.126]:6061 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728352AbfHSVx0 (ORCPT ); Mon, 19 Aug 2019 17:53:26 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Aug 2019 14:53:24 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,406,1559545200"; d="scan'208";a="189658795" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga002.jf.intel.com with ESMTP; 19 Aug 2019 14:53:23 -0700 Date: Mon, 19 Aug 2019 14:53:23 -0700 From: Ira Weiny To: Jason Gunthorpe Cc: Dave Chinner , Jan Kara , Andrew Morton , Dan Williams , Matthew Wilcox , Theodore Ts'o , John Hubbard , Michal Hocko , linux-xfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH v2 00/19] RDMA/FS DAX truncate proposal V1,000,002 ;-) Message-ID: <20190819215322.GA2839@iweiny-DESK2.sc.intel.com> References: <20190809225833.6657-1-ira.weiny@intel.com> <20190814101714.GA26273@quack2.suse.cz> <20190814180848.GB31490@iweiny-DESK2.sc.intel.com> <20190815130558.GF14313@quack2.suse.cz> <20190816190528.GB371@iweiny-DESK2.sc.intel.com> <20190817022603.GW6129@dread.disaster.area> <20190819063412.GA20455@quack2.suse.cz> <20190819092409.GM7777@dread.disaster.area> <20190819123841.GC5058@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190819123841.GC5058@ziepe.ca> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 19, 2019 at 09:38:41AM -0300, Jason Gunthorpe wrote: > On Mon, Aug 19, 2019 at 07:24:09PM +1000, Dave Chinner wrote: > > > So that leaves just the normal close() syscall exit case, where the > > application has full control of the order in which resources are > > released. We've already established that we can block in this > > context. Blocking in an interruptible state will allow fatal signal > > delivery to wake us, and then we fall into the > > fatal_signal_pending() case if we get a SIGKILL while blocking. > > The major problem with RDMA is that it doesn't always wait on close() for the > MR holding the page pins to be destoyed. This is done to avoid a > deadlock of the form: > > uverbs_destroy_ufile_hw() > mutex_lock() > [..] > mmput() > exit_mmap() > remove_vma() > fput(); > file_operations->release() > ib_uverbs_close() > uverbs_destroy_ufile_hw() > mutex_lock() <-- Deadlock > > But, as I said to Ira earlier, I wonder if this is now impossible on > modern kernels and we can switch to making the whole thing > synchronous. That would resolve RDMA's main problem with this. I'm still looking into this... but my bigger concern is that the RDMA FD can be passed to other processes via SCM_RIGHTS. Which means the process holding the pin may _not_ be the one with the open file and layout lease... Ira