> I've seen the panic triggered by assertion at uvm_bio.c:257 on both
> netwinder and shark (both diskless):
> 
>          KASSERT(umap->refcount != 0);
> 
> I reliably get it running a test suite that executes a bunch of
> commands with output to file.  I get it when the output file is either
> on nfs or mfs.
> 
> I have just reproduced the same panic with:
> 
> $ yes | sed 1000000q | while read; do				\
>     ( echo -n 1 >>XXX; echo -n 2 >>XXX; echo -n 3 >>XXX );	\
> done
> 
> 
> Anyone seen this?

Yep,  I get this almost every time I try to do a full bootstrap and 
testrun of gcc.  It's reported in port-arm/23581 as item 2 -- in that case 
the panic was on an FFS local disk.

Debugging this is complicated by the fact that getting a panic dump on ARM 
is currently broken.  I have a patch for that which I'll be testing out 
tomorrow (hopefully); my first attempt was somewhat buggy.