On Mon, May 5, 2014 at 12:21 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Wed, 23 Apr 2014 10:02:00 -0700 Dan Williams <dan.j.williams@xxxxxxxxx> > wrote: > >> On Wed, Apr 23, 2014 at 12:07 AM, NeilBrown <neilb@xxxxxxx> wrote: >> > On Fri, 11 Apr 2014 17:41:12 +0530 "Manibalan P" <pmanibalan@xxxxxxxxxxxxxx> >> > wrote: >> > >> >> Hi Neil, >> >> >> >> Also, I found the data corruption issue on RHEL 6.5. >> >> >> >> For your kind attention, I up-ported the md code [raid5.c + raid5.h] >> >> from FC11 kernel to CentOS 6.4, and there is no mis-compare with the >> >> up-ported code. >> > >> > This narrows it down to between 2.6.29 and 2.6.32 - is that correct? >> > >> > So it is probably the change to RAID6 to support async parity calculations. >> > >> > Looking at the code always makes my head spin. >> > >> > Dan : have you any ideas? >> > >> > It seems that writing to a double-degraded RAID6 while it is recovering to >> > a space can trigger data corruption. >> > >> > 2.6.29 works >> > 2.6.32 doesn't >> > 3.8.0 still doesn't. >> > >> > I suspect async parity calculations. >> >> I'll take a look. I've had cleanups of that code on my backlog for "a >> while now (TM)". > > > Hi Dan, > did you have a chance to have a look? > > I've been consistently failing to find anything. > > I have a question though. > If we set up a chain of async dma handling via: > ops_run_compute6_2 then ops_bio_drain then ops_run_reconstruct > > is it possible for the ops_complete_compute callback set up by > ops_run_compute6_2 to be called before ops_run_reconstruct has been scheduled > or run? In the absence of a dma engine we never run asynchronously, so we will *always* call ops_complete_compute() before ops_run_reconstruct() in the synchronous acse. This looks confused. We're certainly leaking an uptodate state prior to the completion of the write. > If so, there seems to be some room for confusion over the setting for > R5_UPTODATE on blocks that are being computed and then drained to. Both will > try to set the flag, so it could get set before reconstruction has run. > > I can't see that this would cause a problem, but then I'm not entirely sure > why we clear R5_UPTODATE when we set R5_Wantdrain. Let me see what problems this could be causing. I'm thinking we should be protected by the global ->reconstruct_state, but something is telling me we do depend on R5_UPTODATE being consistent with the ongoing stripe operation. -- Dan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
