Processes can sleep in do_get_write_access(), waiting for buffers to be
removed from the BJ_Shadow state.  We did this by doing a wake_up_buffer() in
the commit path and sleeping on the buffer in do_get_write_access().

With the filtered bit-level wakeup code this doesn't work properly any more -
the wake_up_buffer() accidentally wakes up tasks which are sleeping in
lock_buffer() as well.  Those tasks now implicitly assume that the buffer came
unlocked.  Net effect: Bogus I/O errors when reading journal blocks, because
the buffer isn't up to date yet.  Hence the recently spate of journal_bmap()
failure reports.

The patch creates a new jbd-private BH flag purely for this wakeup function.
So a wake_up_bit(..., BH_Unshadow) doesn't wake up someone who is waiting for
a wake_up_bit(BH_Lock).

JBD was the only user of wake_up_buffer(), so remove it altogether.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>