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Re: [Xen-devel] segfault in VM - FIXED!

On Jul 23, 2004, at 12:01 PM, Keir Fraser wrote:

Okay, so I found that the problem is due to overly-aggressive merging
of block requests in the IDE driver. The code assumes that if buffers
are adjacent in virtual or physical address space then they can be
merged --- this isn't always the case over Xen since those physical
addresses may map to different real machine pages.

And there was much rejoicing!

Thanks Keir for working so hard on digging this problem out and getting a fix in.

Other than the doms not dying after a halt, which you said you checked in a fix, and the occasional strange unbalanced dom scheduling, which I understand the scheduler is being worked on, the -unstable branch has worked very well for me so far. (Well, outside of the random crashes... :)

I'll do a pull tonight when I get home and rebuild everything and start hammering on it some more.

I've checked in a fix that I think is safe for IDE --- in the
occasional instances that a merged scatter-gather list is invalid, we
should now cause IDE to fall back to a super-safe mode (basically
PIO). On my system this happens so occasionally that performance
shouldn't be affected.

Does it revert back to "normal" behaviour for consequent operations? i.e. is the "basically PIO" mode just for the operation that fails?

What we need now is some more checking, particularly with SCSI block
devices, to see whether there are any more bugs to shake out.

Would it help at all for me to set up a box as ide-scsi, or is it strictly the data path inside the individual SCSI drivers that could cause problems?

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