Re: [PATCH 04/12] fs: ceph: CURRENT_TIME with ktime_get_real_ts()

On Fri, Jun 2, 2017 at 12:10 PM, Yan, Zheng <ukernel(a)gmail.com&gt; wrote: > On Fri, Jun 2, 2017 at 5:45 PM, Arnd Bergmann <arnd(a)arndb.de&gt; wrote: >> On Fri, Jun 2, 2017 at 4:09 AM, Yan, Zheng <ukernel(a)gmail.com&gt; wrote: >>> On Fri, Jun 2, 2017 at 8:57 AM, Deepa Dinamani <deepa.kernel(a)gmail.com&gt; wrote: >>>> On Thu, Jun 1, 2017 at 5:36 PM, John Stultz <john.stultz(a)linaro.org&gt; wrote: >>>>> On Thu, Jun 1, 2017 at 5:26 PM, Yan, Zheng <ukernel(a)gmail.com&gt; 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/24f54cd18e195a002ee3d2ab50dbc9... Looks good to me. In case anyone cares: Acked-by: Arnd Bergmann <arnd(a)arndb.de&gt; >> 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).

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