On Mon, Jun 26 2017 at 9:47am -0400, Eric Ren <zren@xxxxxxxx> wrote: > Hi, > > On 06/26/2017 06:55 PM, Eric Ren wrote: > >Hi Zdenek, > > > > > >On 06/26/2017 05:46 PM, Zdenek Kabelac wrote: > >>Dne 26.6.2017 v 11:08 Eric Ren napsal(a): > >>> > >>[... snip...] > >> > >>Hi > >> > >>Which kernel version is this ? > >> > >>I'd thought we've already fixed this BZ for old mirrors: > >>https://bugzilla.redhat.com/show_bug.cgi?id=1382382 > >> > >>There similar BZ for md-raid based mirrors (--type raid1) > >>https://bugzilla.redhat.com/show_bug.cgi?id=1416099 > >My base kernel version is 4.4.68, but with this 2 latest fixes applied: > > > >""" > >Revert "dm mirror: use all available legs on multiple failures" > >dm io: fix duplicate bio completion due to missing ref count > > I have a confusion about this "dm io..." fix. The fix itself is good. > > Without it, a mkfs.ext4 on a mirrored dev whose primary mirror dev > has failed, will crash the kernel with the discard operation from mkfs.ext4. > However, mkfs.ext4 can succeed on a healthy mirrored device. This > is the thing I don't understand, because no matter the mirrored device is > good or not, there's always a duplicate bio completion before having this > this fix, thus write_callback() will be called twice, crashing will > occur on the > second write_callback(): No, there is only a duplicate bio completion if the error path is taken (e.g. underlying device doesn't support discard). > """ > static void write_callback(unsigned long error, void *context) > { > unsigned i; > struct bio *bio = (struct bio *) context; > struct mirror_set *ms; > int should_wake = 0; > unsigned long flags; > > ms = bio_get_m(bio)->ms; ====> NULL pointer at the > duplicate completion > bio_set_m(bio, NULL); > """ > > If no this fix, I expected the DISCARD IO would always crash the > kernel, but it's not true when > the mirrored device is good. Hope someone happen to know the reason > can give some hints ;-P If the mirror is healthy then only one completion is returned to dm-mirror (via write_callback). The problem was the error patch wasn't managing the reference count as needed. Whereas dm-io's normal discard IO path does. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
