From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e31.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id mB21AwxF014326 for ; Mon, 1 Dec 2008 18:10:58 -0700 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id mB21C9FQ165076 for ; Mon, 1 Dec 2008 18:12:09 -0700 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id mB21C8Ur009351 for ; Mon, 1 Dec 2008 18:12:09 -0700 Subject: Re: [RFC v10][PATCH 09/13] Restore open file descriprtors From: Dave Hansen In-Reply-To: <49345086.4@cs.columbia.edu> References: <1227747884-14150-1-git-send-email-orenl@cs.columbia.edu> <1227747884-14150-10-git-send-email-orenl@cs.columbia.edu> <20081128112745.GR28946@ZenIV.linux.org.uk> <1228159324.2971.74.camel@nimitz> <49344C11.6090204@cs.columbia.edu> <1228164873.2971.95.camel@nimitz> <49345086.4@cs.columbia.edu> Content-Type: text/plain Date: Mon, 01 Dec 2008 17:12:06 -0800 Message-Id: <1228180326.2971.128.camel@nimitz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Oren Laadan Cc: linux-api@vger.kernel.org, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Thomas Gleixner , Al Viro , "H. Peter Anvin" , Ingo Molnar , Andrew Morton List-ID: On Mon, 2008-12-01 at 16:00 -0500, Oren Laadan wrote: > Dave Hansen wrote: > > On Mon, 2008-12-01 at 15:41 -0500, Oren Laadan wrote: > >>>>> + fd = cr_attach_file(file); /* no need to cleanup 'file' below */ > >>>>> + if (fd < 0) { > >>>>> + filp_close(file, NULL); > >>>>> + ret = fd; > >>>>> + goto out; > >>>>> + } > >>>>> + > >>>>> + /* register new tuple in hash table */ > >>>>> + ret = cr_obj_add_ref(ctx, file, parent, CR_OBJ_FILE, 0); > >>>>> + if (ret < 0) > >>>>> + goto out; > >>>> Who said that file still exists at that point? > >> Correct. This call should move higher up befor ethe call to cr_attach_file() > > > > Is that sufficient? It seems like we're depending on the fd's reference > > to the 'struct file' to keep it valid in the hash. If something happens > > to the fd (like the other thread messing with it) the 'struct file' can > > still go away. > > > > Shouldn't we do another get_file() for the hash's reference? > > When a shared object is inserted to the hash we automatically take another > reference to it (according to its type) for as long as it remains in the > hash. See: 'cr_obj_ref_grab()' and 'cr_obj_ref_drop()'. So by moving that > call higher up, we protect the struct file. We also need to document that we depend on this reference in the hash to keep the object around. Take a look at cr_read_fd_data(). Once that cr_attach_file() has been performed, the only thing keeping the 'file' around is the hash reference. If someone happened to remove it from the hash, the vfs_llseek() below would be bogus. I don't know how we document that the hash is one-way: writes only and no later deletions. -- Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org