On Tue, Jun 26, 2018 at 2:31 PM, Kani, Toshi <toshi.kani@xxxxxxx> wrote: > On Tue, 2018-06-26 at 14:28 -0700, Dan Williams wrote: >> On Tue, Jun 26, 2018 at 2:23 PM, Kani, Toshi <toshi.kani@xxxxxxx> wrote: >> > On Tue, 2018-06-26 at 14:02 -0700, Dan Williams wrote: >> > > On Tue, Jun 26, 2018 at 1:54 PM, Kani, Toshi <toshi.kani@xxxxxxx> wrote: >> >> [..] >> > > > When this dm change was made, the pmem driver supported DAX for both raw >> > > > and memory modes (note: sector mode does not use the pmem driver). I >> > > > think the issue was introduced when we dropped DAX support from raw >> > > > mode. >> > > >> > > Still DAX with raw mode never really worked any way. It was also >> > > something that was broken from day one. So what happens to someone who >> > > happened to avoid all the problems with page-less DAX and enabled >> > > device-mapper on top? That failure mode detail needs to be added to >> > > this changelog if we want to propose this for -stable. >> > >> > My point is that the behavior should be consistent between pmem and >> > device-mapper. When -o dax succeeds on a pmem, then it should succeed >> > on a device-mapper on top of that pmem. >> > >> > Has the drop of dax support from raw mode made to -stable back to the >> > baseline accepted 545ed20e6df6? It will introduce inconsistency, >> > otherwise. >> >> That commit, 569d0365f571 "dax: require 'struct page' by default for >> filesystem dax", has not been tagged for -stable. > > Then, Fixes tag should be set to 569d0365f571 to keep the behavior > consistent. Sure, and the failure mode is...? I'm thinking the commit log should say: "Starting with commit 569d0365f571 "dax: require 'struct page' by default for filesystem dax", dax is no longer supported for page-less configurations. However, device-mapper sees the QUEUE_FLAG_DAX still being set and falsely assumes that DAX is enabled, this leads to <insert user visible failure mode details here>"
