Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751205AbdFBLdh (ORCPT ); Fri, 2 Jun 2017 07:33:37 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:33762 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbdFBLdd (ORCPT ); Fri, 2 Jun 2017 07:33:33 -0400 MIME-Version: 1.0 In-Reply-To: References: <1491613030-11599-1-git-send-email-deepa.kernel@gmail.com> <1491613030-11599-5-git-send-email-deepa.kernel@gmail.com> From: Arnd Bergmann Date: Fri, 2 Jun 2017 13:33:32 +0200 X-Google-Sender-Auth: Z_wkaLOSCvMQmI4Xdg7U1Y-loZw Message-ID: Subject: Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() To: "Yan, Zheng" Cc: Deepa Dinamani , John Stultz , Linux Kernel Mailing List , Andrew Morton , Thomas Gleixner , Al Viro , gregkh , "Dilger, Andreas" , "J. Bruce Fields" , Chris Mason , David Miller , David Sterba , Evgeniy Dushistov , Eric Paris , Jaegeuk Kim , Josef Bacik , Jeff Layton , James Simmons , Ingo Molnar , "Drokin, Oleg" , Paul Moore , Steven Rostedt , yuchao0@huawei.com, ceph-devel , devel@driverdev.osuosl.org, linux-audit@redhat.com, linux-btrfs , linux-cifs@vger.kernel.org, "Linux F2FS DEV, Mailing List" , Linux FS-devel Mailing List , linux-mtd , LSM List , Lustre Development List , Networking , samba-technical@lists.samba.org, y2038 Mailman List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3192 Lines: 64 On Fri, Jun 2, 2017 at 1:18 PM, Yan, Zheng wrote: > On Fri, Jun 2, 2017 at 6:51 PM, Arnd Bergmann wrote: >> On Fri, Jun 2, 2017 at 12:10 PM, Yan, Zheng wrote: >>> On Fri, Jun 2, 2017 at 5:45 PM, Arnd Bergmann wrote: >>>> On Fri, Jun 2, 2017 at 4:09 AM, Yan, Zheng wrote: >>>>> On Fri, Jun 2, 2017 at 8:57 AM, Deepa Dinamani wrote: >>>>>> On Thu, Jun 1, 2017 at 5:36 PM, John Stultz wrote: >>>>>>> On Thu, Jun 1, 2017 at 5:26 PM, Yan, Zheng wrote: >>>> >>>> I believe the bug you see is the result of the two timestamps >>>> currently being almost guaranteed to be different in the latest >>>> kernels. >>>> Changing r_stamp to use current_kernel_time() will make it the >>>> same value most of the time (as it was before Deepa's patch), >>>> but when the timer interrupt happens between the timestamps, >>>> the two are still different, it's just much harder to hit. >>>> >>>> I think the proper solution should be to change __ceph_setattr() >>>> in a way that has req->r_stamp always synchronized with i_ctime. >>>> If we copy i_ctime to r_stamp, that will also take care of the >>>> future issues with the planned changes to current_time(). >>>> >>> I already have a patch >>> https://github.com/ceph/ceph-client/commit/24f54cd18e195a002ee3d2ab50dbc952fd9f82af >> >> Looks good to me. In case anyone cares: >> Acked-by: Arnd Bergmann >> >>>> The part I don't understand is what else r_stamp (i.e. the time >>>> stamp in ceph_msg_data with type== >>>> CEPH_MSG_CLIENT_REQUEST) is used for, other than setting >>>> ctime in CEPH_MDS_OP_SETATTR. >>>> >>>> Will this be used to update the stored i_ctime for other operations >>>> too? If so, we would need to synchronize it with the in-memory >>>> i_ctime for all operations that do this. >>>> >>> >>> yes, mds uses it to update ctime of modified inodes. For example, >>> when handling mkdir, mds set ctime of both parent inode and new inode >>> to r_stamp. >> >> I see, so we may have a variation of that problem there as well: From >> my reading of the code, the child inode is not in memory yet, so >> that seems fine, but I could not find where the parent in-memory inode >> i_ctime is updated in ceph, but it is most likely not the same as >> req->r_stamp (assuming it gets updated at all). > > i_ctime is updated when handling request reply, by ceph_fill_file_time(). > __ceph_setattr() can update the in-memory inode's ctime after request > reply is received. The difference between ktime_get_real_ts() and > current_time() can be larger than round-trip time of request. So it's > still possible that __ceph_setattr() make ctime go back. But the __ceph_setattr() problem should be fixed by your patch, right? What I meant is another related problem in ceph_mkdir() where the i_ctime field of the parent inode is different between the persistent representation in the mds and the in-memory representation. Arnd >> Would it make sense require all callers of ceph_mdsc_do_request() >> to update r_stamp at the same time as i_ctime to keep them in sync?