On Fri, Jun 2, 2017 at 7:33 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Fri, Jun 2, 2017 at 1:18 PM, Yan, Zheng <ukernel@xxxxxxxxx> wrote: >> 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. > > 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. > I don't see any problem in mkdir case. Parent inode's i_ctime in mds is set to r_stamp. When client receives request reply, it set its in-memory inode's ctime to the same time stamp. Regards Yan, Zheng > 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? _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
