Hey Eric, On Fri, Jun 14, 2013 at 02:54:24PM -0500, Eric Sandeen wrote: > On 6/14/13 2:44 PM, Ben Myers wrote: > > Hey Eric, > > > > On Fri, Jun 14, 2013 at 02:18:20PM -0500, Eric Sandeen wrote: > >> On 6/14/13 2:08 PM, Ben Myers wrote: > >>> On Fri, Jun 14, 2013 at 11:15:41AM -0500, Eric Sandeen wrote: > >>>> Ben, isn't it the case that the corruption would only happen if > >>>> log replay failed for some reason (as has always been the case, > >>>> verifier or not), but with the verifier in place, it kills replay > >>>> even w/o other problems due to a logical problem with the > >>>> (recently added) verifiers? > >>> > >>> It seems like the verifier prevented corruption from hitting disk during > >>> log replay. > >> > >> It detected a an inconsistent *interim* state during replay, which is > >> always made correct by log replay completion. But it *stopped* that log > >> replay completion. And caused log replay to fail. And mount to fail. > >> This is *new* behavior, and bad. > >> > >> As I understand it. > >> > >>> It is enforcing a partial replay up to the point where the > >>> corruption occurred. Now you should be able to zero the log and the > >>> filesystem is not corrupted. > >>> > >>>> IOW - this seems like an actual functional regression due to the > >>>> addition of the verifier, and dchinner's patch gets us back > >>>> to the almost-always-fine state we were in prior to the change. > >>> > >>> Oh, the spin doctor is *in*! > >> > >> This is not spin. > >> > >>> This isn't a logical problem with the verifier, it's a logical problem > >>> with log replay. We need to find a way for recovery to know whether a > >>> given transaction should be replayed. Fixing that is nontrivial. > >> > >> Right. > >> > >> And it's been around for years. The verifier now detects that > >> interim state, and makes things *worse* than they would be had log > >> replay been allowed to continue. > >> > >> Fixing the interim state may be nontrivial; allowing log replay > >> to continue to a consistent state as it always has *is* trivial, > >> it's what's done in Dave's small patch. > >> > >>>> As we're at -rc6, it seems quite reasonable to me as a quick > >>>> fix to just short-circuit it for now. > >>> > >>> If we're talking about a short term fix, that's fine. This should be > >>> conditional on CONFIG_XFS_DEBUG and marked as such. > >>> > >>> Long term, removing the verifiers is the wrong thing to do here. We > >>> need to fix the recovery bug and then remove this temporary workaround. > >>> > >>>> If you have time to analyze dave's metadump that's cool, but > >>>> this seems like something that really needs to be addressed > >>>> before 3.10 gets out the door. > >>> > >>> If this really is a day one bug then it's been out the door almost > >>> twenty years. And you want to hurry now? ;) > >> > >> We seem to be talking past each other. > >> > >> The corrupted interim state has been around for years. Up until > >> now, log replay completion left things in perfect state. > >> > >> The verifier now *breaks replay* at that interim point. > >> Were it allowed to continue, everything would be fine. > >> > >> As things stand, it is not fine, and this is a recent change > >> which Dave is trying to correct. > >> > >> Leaving it in place will cause filesystems which were replaying > >> logs just fine until recently to now fail with no good way out. > > > > That is consistent with my understanding of the problem... > > > > Unfortunately log replay is broken. The verifier has detected this and stopped > > replay. Ideally the solution would be to fix log replay, but that is going to > > take some time. So, in the near term we're just going to disable the verifier > > to allow replay to complete. > > Right, that's what we're hoping - for 3.10 right? Yep. But it should also go back through -stable. > Maybe the talking-past-each-other was only that part. I thought you didn't > want to disable it for now. I didn't want to disable it. That was yesterday. Mark set me straight on how easy this should be to hit. > > I'm suggesting that this disabling be done conditionally on CONFIG_XFS_DEBUG so > > that developers still have a chance at hitting the log replay problem, > > so that real-world users will still feel the pain ...? > > Or did you say that backwards (really only *disabling* it under debug?) > > Ok, confirmed on IRC you mean to disable it if *NOT* debug, enable it > under debug. Right. > > and a > > comment should be added explaining that we've disabled the verifier due to a > > specific bug as a temporary workaround and we'll re-enable the verifier once > > it's fixed. I'll update the patch and repost. > > Maybe if the verifiers were *on* under debug that'd make sense. Sorry for the confusion. > I think putting it under the config is overkill, since anyone who wants > to fix it is surely capable of re-enabling it in the code. But if that > avoids an impasse, I don't much care. Great. Apparently I'm being pedantic today. I'd like it to be clear that we intend for this to be a temporary workaround.... > > Are you guys arguing that the log replay bug should not be fixed? > > Speaking for myself, I'm not arguing that, not at all. > (not that I know how to fix it, either) ...until log replay is fixed. Hell. I'll just pull it in as-is. Reviewed-by: Ben Myers <bpm@xxxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
