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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 AB006C433FF for ; Mon, 12 Aug 2019 21:16:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EB55206C2 for ; Mon, 12 Aug 2019 21:16:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726845AbfHLVQE (ORCPT ); Mon, 12 Aug 2019 17:16:04 -0400 Received: from mga06.intel.com ([134.134.136.31]:44879 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726663AbfHLVQE (ORCPT ); Mon, 12 Aug 2019 17:16:04 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Aug 2019 14:15:38 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,378,1559545200"; d="scan'208";a="376081222" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by fmsmga006.fm.intel.com with ESMTP; 12 Aug 2019 14:15:37 -0700 Date: Mon, 12 Aug 2019 14:15:37 -0700 From: Ira Weiny To: Jason Gunthorpe Cc: Andrew Morton , Dan Williams , Matthew Wilcox , Jan Kara , Theodore Ts'o , John Hubbard , Michal Hocko , Dave Chinner , 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 16/19] RDMA/uverbs: Add back pointer to system file object Message-ID: <20190812211537.GE20634@iweiny-DESK2.sc.intel.com> References: <20190809225833.6657-1-ira.weiny@intel.com> <20190809225833.6657-17-ira.weiny@intel.com> <20190812130039.GD24457@ziepe.ca> <20190812172826.GA19746@iweiny-DESK2.sc.intel.com> <20190812175615.GI24457@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190812175615.GI24457@ziepe.ca> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Mon, Aug 12, 2019 at 02:56:15PM -0300, Jason Gunthorpe wrote: > On Mon, Aug 12, 2019 at 10:28:27AM -0700, Ira Weiny wrote: > > On Mon, Aug 12, 2019 at 10:00:40AM -0300, Jason Gunthorpe wrote: > > > On Fri, Aug 09, 2019 at 03:58:30PM -0700, ira.weiny@intel.com wrote: > > > > From: Ira Weiny > > > > > > > > In order for MRs to be tracked against the open verbs context the ufile > > > > needs to have a pointer to hand to the GUP code. > > > > > > > > No references need to be taken as this should be valid for the lifetime > > > > of the context. > > > > > > > > Signed-off-by: Ira Weiny > > > > drivers/infiniband/core/uverbs.h | 1 + > > > > drivers/infiniband/core/uverbs_main.c | 1 + > > > > 2 files changed, 2 insertions(+) > > > > > > > > diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h > > > > index 1e5aeb39f774..e802ba8c67d6 100644 > > > > +++ b/drivers/infiniband/core/uverbs.h > > > > @@ -163,6 +163,7 @@ struct ib_uverbs_file { > > > > struct page *disassociate_page; > > > > > > > > struct xarray idr; > > > > + struct file *sys_file; /* backpointer to system file object */ > > > > }; > > > > > > The 'struct file' has a lifetime strictly shorter than the > > > ib_uverbs_file, which is kref'd on its own lifetime. Having a back > > > pointer like this is confouding as it will be invalid for some of the > > > lifetime of the struct. > > > > Ah... ok. I really thought it was the other way around. > > > > __fput() should not call ib_uverbs_close() until the last reference on struct > > file is released... What holds references to struct ib_uverbs_file past that? > > Child fds hold onto the internal ib_uverbs_file until they are closed The FDs hold the struct file, don't they? > > > Perhaps I need to add this (untested)? > > > > diff --git a/drivers/infiniband/core/uverbs_main.c > > b/drivers/infiniband/core/uverbs_main.c > > index f628f9e4c09f..654e774d9cf2 100644 > > +++ b/drivers/infiniband/core/uverbs_main.c > > @@ -1125,6 +1125,8 @@ static int ib_uverbs_close(struct inode *inode, struct file *filp) > > list_del_init(&file->list); > > mutex_unlock(&file->device->lists_mutex); > > > > + file->sys_file = NULL; > > Now this has unlocked updates to that data.. you'd need some lock and > get not zero pattern You can't call "get" here because I'm 99% sure we only get here when struct file has no references left... I could be wrong. It took me a while to work through the reference counting so I could have missed something. Ira