Why is mapping->truncate_count atomic?  It's incremented inside i_mmap_lock
(and i_sem), and the reads don't need it to be atomic.

And why smp_rmb() before call to ->nopage?  The compiler cannot reorder the
initial assignment of sequence after the call to ->nopage, and no cpu (yet!)
can read from the future, which is all that matters there.

And delete totally bogus reset of truncate_count from blkmtd add_device.
truncate_count is all about detecting i_size changes: i_size does not change
there; and if it did, the count should be incremented not reset.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>