Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751188AbdFBLS7 (ORCPT ); Fri, 2 Jun 2017 07:18:59 -0400 Received: from mail-ua0-f195.google.com ([209.85.217.195]:34047 "EHLO mail-ua0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbdFBLSz (ORCPT ); Fri, 2 Jun 2017 07:18:55 -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: "Yan, Zheng" Date: Fri, 2 Jun 2017 19:18:53 +0800 Message-ID: Subject: Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts() To: Arnd Bergmann 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: 2823 Lines: 62 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. Regards Yan, Zheng > > 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? > > Arnd