Re: [9fans] pool curalloc bug

[cinap_lenrek@felloff.net]

the problem with curalloc was the following:

poolallocl() allocates, trims, and then adds the resulting
block size to curalloc. and poolfreel() subtracts the blocksize
from curalloc. so far so good. problem is when we try to merge
arenas, the last block in the bottom arena is extended up to
the start of the top arena to encompass the space between,
and then it is trimmed back to its old *data* size. depending
on the size of the gab, the free data might be accounted for in the
Btail datasize or it might get its own free block if it is
big enougth. in the first case, the block size would'v been
increased (we got some extra space at the end) but this was not
accounted for in curalloc. so poolfreel() will subtract a bigger
value than was added to curalloc, hence the underflow.

the fix is to account for the changed block size in curalloc when
merging arenas.

curalloc is also not properly maintained in poolallocalign(),
but thats not in the testcase.

--
cinap