On Fri, Jun 2, 2017 at 6:51 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Fri, Jun 2, 2017 at 12:10 PM, Yan, Zheng <ukernel@xxxxxxxxx> wrote: >> On Fri, Jun 2, 2017 at 5:45 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >>> On Fri, Jun 2, 2017 at 4:09 AM, Yan, Zheng <ukernel@xxxxxxxxx> wrote: >>>> On Fri, Jun 2, 2017 at 8:57 AM, Deepa Dinamani <deepa.kernel@xxxxxxxxx> wrote: >>>>> On Thu, Jun 1, 2017 at 5:36 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote: >>>>>> On Thu, Jun 1, 2017 at 5:26 PM, Yan, Zheng <ukernel@xxxxxxxxx> 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 <arnd@xxxxxxxx> > >>> 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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
