[Crash-utility] Crash physical search on live session not recommended :-)

[Bob Montgomery]

On Thu, 2011-02-24 at 15:18 +0000, Dave Anderson wrote:
> 
> ----- Original Message -----
> > While testing my search patch, I kicked off an unconstrained physical
> > search on a live session and hung the machine so thoroughly that it
> > required a visit to the machine room to physically unplug it to get the
> > remote console back up. Coincidence? Or should physical address search
> > on a live session be constrained somehow for safety?
> > 
> > Bob Montgomery
> 
> Maybe so -- I had no problem with any of the systems I've tested it on.
> 
> Is it always reproducible on that system?
I'll let you know when I get a chance to test again.  If it fails like
it did before, it will tie up two of us for the 10-minute walk to the
machine room where I don't currently have access :-).
> 
> And does that system use /dev/mem or /dev/crash?
/dev/mem

> 
> It would be interesting to know if a particular physical address caused it,
> or if there are physical pages that are read that are *not* read when an 
> unconstrained kernel virtual search is done?

The pages should have been copied to the buffer a page at a time, right? 
So the search access pattern within the buffer shouldn't affect how
physical memory was accessed (I was thinking that string search's byte
aligned access might have mattered).   Could the physical search come
up with a page in /dev/mem that wouldn't also be accessed in the
identity-mapped virtual case?


Bob M.

> Dave
> 
>