Re: Raid-6 hang on write.

[Brad Campbell]

Neil Brown wrote:
> On Friday February 25, brad@xxxxxxxxxxx wrote:
>
> > Turning on debugging in raid6main.c and md.c make it much harder to hit. So I'm assuming something 
> > timing related.
> >
> > raid6d --> md_check_recovery --> generic_make_request --> make_request --> get_active_stripe
>
>
> Yes, there is a real problem here.  I see if I can figure out the best
> way to remedy it...
> However I think you reported this problem against a non "-mm" kernel,
> and the path from md_check_recovery to generic_make_requests only
> exists in "-mm".
>
> Could you please confirm if there is a problem with
>     2.6.11-rc4-bk4->bk10

There is (was). I have three kernels I was testing against. 2.6.11-rc4-bk4, 2.6.11-rc4-bk10 and 
2.6.11-rc4-mm1. I moved onto 2.6.11-rc4-mm1 for my main debugging (inserting lots of printks and 
generally doing stuff that was going to crash). I hope to reproduce the faults against the vanilla 
2.6.11-rc4 kernels and I'm now testing with 2.6.11-rc5-bk2.

As per the original bug report, 2.6.11-rc4-bk(4/10) locked in [<c0268574>] 
get_active_stripe+0x224/0x260. Although unlike -mm1 I'm not sure of the sequence of events that 
caused it and it's not anywhere as easy to hit. I am willing to investigate as time allows however.

Testing 2.6.11-rc5-bk2 and it of course is flatly refusing to misbehave. I'll keep beating on it for 
a couple of days and after writing 3TB with 2.6.11-rc5-bk2, I'll go back to the older kernels and 
try and reproduce the failure there. It *did* lockup 4 times in a row in get_active_stripe on the 
older non -mm kernels.

Regards,
Brad
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