softdep panic while low on memory during "make buildworld"

[Peter Avalos]

On Fri, Jan 25, 2008 at 11:51:18AM -0800, Matthew Dillon wrote:
> 
>     This has happened to me on a virtual machine too.
> 

It happens to me on a real live kernel.

>     First, some background... softdeps holds onto buffers which have
>     dependancies, so if buf_deallocate() is EVER called on a softdep
>     bp, all softdep's callback does is panic because the situation is
>     not supposed to happen.
> 
>     I haven't been able to track it down yet.  The panic does not occur
>     very often at all and I was in the middle of some HAMMER debugging
>     when I got it and didn't want to switch modes, so to speak :-).  It
>     has only happened to me once so far.
> 
>     The VKERNEL's timing is very different from a normal kernel, and
>     most people run it with significantly less 'memory' then a real 
>     kernel (I specify 64MB for the one I test HAMMER in, similar to
>     the 64MB vkernel you were using), and those differences tend to bring
>     out software bugs that are not normally apparent when running a
>     real kernel.
> 

I have 2G of RAM, and I'm able to reproduce this if I really stress the
machine.  I've turned off softupdates since this was killing my
productivity.
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