my system is arm 926, kernel version is 2.6.12.6, the data cache is virtually
tagged and virtually indexed and with no hw cache coherency. my CPU features the
data cache write allocate-> when doing store, the cache line of the destination
address is loaded to data cache.
  when enabling the write allocate, I got data corruption with the
xfs. the scenario is that the xfs allocates large buffer (for reading
the log records) using vmalloc, and the low level driver (raid) copies
the data to the bio vectors using the linear address, since the write
allocate is enabled,  the correct data remains on the data cache with
the linear address tag, when the IO completes, the xfs access the data
with using the vmalloc virtual address, which is different than the
kernel linear address, thus it will get a stale data!.