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Wed, 11 Sep 2019 01:19:57 -0700 (PDT) Received: from ziepe.ca ([148.69.85.38]) by smtp.gmail.com with ESMTPSA id a13sm36163114wrf.73.2019.09.11.01.19.56 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 11 Sep 2019 01:19:56 -0700 (PDT) Received: from jgg by jggl.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1i7xr1-0002Mq-Vn; Wed, 11 Sep 2019 05:19:55 -0300 Date: Wed, 11 Sep 2019 05:19:55 -0300 From: Jason Gunthorpe To: Ira Weiny 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: <20190911081955.GA9070@ziepe.ca> References: <20190812130039.GD24457@ziepe.ca> <20190812172826.GA19746@iweiny-DESK2.sc.intel.com> <20190812175615.GI24457@ziepe.ca> <20190812211537.GE20634@iweiny-DESK2.sc.intel.com> <20190813114842.GB29508@ziepe.ca> <20190813174142.GB11882@iweiny-DESK2.sc.intel.com> <20190813180022.GF29508@ziepe.ca> <20190813203858.GA12695@iweiny-DESK2.sc.intel.com> <20190814122308.GB13770@ziepe.ca> <20190904222549.GC31319@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904222549.GC31319@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Sep 04, 2019 at 03:25:50PM -0700, Ira Weiny wrote: > On Wed, Aug 14, 2019 at 09:23:08AM -0300, Jason Gunthorpe wrote: > > On Tue, Aug 13, 2019 at 01:38:59PM -0700, Ira Weiny wrote: > > > On Tue, Aug 13, 2019 at 03:00:22PM -0300, Jason Gunthorpe wrote: > > > > On Tue, Aug 13, 2019 at 10:41:42AM -0700, Ira Weiny wrote: > > > > > > > > > And I was pretty sure uverbs_destroy_ufile_hw() would take care of (or ensure > > > > > that some other thread is) destroying all the MR's we have associated with this > > > > > FD. > > > > > > > > fd's can't be revoked, so destroy_ufile_hw() can't touch them. It > > > > deletes any underlying HW resources, but the FD persists. > > > > > > I misspoke. I should have said associated with this "context". And of course > > > uverbs_destroy_ufile_hw() does not touch the FD. What I mean is that the > > > struct file which had file_pins hanging off of it would be getting its file > > > pins destroyed by uverbs_destroy_ufile_hw(). Therefore we don't need the FD > > > after uverbs_destroy_ufile_hw() is done. > > > > > > But since it does not block it may be that the struct file is gone before the > > > MR is actually destroyed. Which means I think the GUP code would blow up in > > > that case... :-( > > > > Oh, yes, that is true, you also can't rely on the struct file living > > longer than the HW objects either, that isn't how the lifetime model > > works. > > Reviewing all these old threads... And this made me think. While the HW > objects may out live the struct file. > > They _are_ going away in a finite amount of time right? It is not like they > could be held forever right? Yes, at least until they become shared between FDs Jason